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Professor Liz Carpenter

Research Area: Protein Science and Structural Biology
Technology Exchange: Crystallography, Drug discovery and Protein interaction
Scientific Themes: Protein Science & Structural Biology and Physiology, Cellular & Molecular Biology
Keywords: Membrane proteins, X-ray crystallography, Protein structure, ion channels, high throughput methods and drug design
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Membrane proteins are the gateways to the cell. All cells and organelles are surrounded by an oily, impermeable lipid bilayer and many small molecules can only cross this barrier by passing through protein molecules embedded in the bilayer. Many nutrients, ions, waste products and even DNA and proteins enter and leave cells only via proteins which are tightly controlled, thus maintaining the integrity of the cell. Communication between cells is also mediated by these proteins often by binding signaling molecules outside cells and amplifying the signal by triggering chemical reactions inside the cell. These diverse functions are fulfilled by a huge variety of membrane proteins, in fact approximately 15% of all the genes in the human genome code for these proteins. Given their location on the surfaces of cells, it is not surprising that membrane proteins are often found to be the targets for drugs, such as the calcium channel blockers used to treat heart disease and potassium channel blockers which are used in diabetes treatment. Indeed membrane proteins are involved in the development of many diseases, including heart disease, cancer, cystic fibrosis, Alzheimer’s, Parkinson’s and other neurological diseases, kidney disease and epilepsy.

My group at the structural Genomics Consortium in Oxford aims to solve the three dimensional structures of human membrane proteins using X-ray crystallography. We purify proteins, pursuad them to form crystals, and then expose them to a beam of X-rays. The resulting diffraction patterns can then be used to understand the positions of all the atoms in the protein. We then study the structures in complex with inhibitors and drugs, using this information to improve and extend the available treatments for disease. There are less than 50 structures of human membrane proteins known and we therefore seak to develop methods to make this process more efficient. In the past four years we have established a working high-throughput system for the producing human membrane proteins for structural studies.

The IMP group at the SGC studies proteins from a variety membrane protein families, including ion channels enzymes and ABC transporters. To date we have solved structures of of proteins in three different areas:

1. We solved the first structure of a human ABC transporter, ABCB10, a mitochondrial protein which is important for heme production and for resistance of mitochondria to oxidative stress.

2. Premature ageing syndromes can be caused by a failure in the processing of the lamin proteins, which form a network of fibres underlying the nuclear membrane within cells. We have solved the structure of a zinc metalloprotease, ZMPSTE24, which is responsible for two steps in this processing. This structure has allowed us to see how mutations in the ZMPSTE24 protein can lead to premature ageing diseases, which provide a model for normal ageing.

3. Recently we have solved and deposited the structure of a human ion channel, TREK-2, one of the family of K2P proteins which are responsible for the background leak current that helps to maintain the membrane potential and also are susceptible to a range of physiological and pharmacological stimuli.

Name Department Institution Country
Professor Juha T Huiskonen Structural Biology Oxford University, Oxford Particle Imaging Centre United Kingdom
Dr Nicola A Burgess-Brown Structural Genomics Consortium Oxford University, Old Road Campus Research Building United Kingdom
Professor Wyatt W Yue Structural Genomics Consortium Oxford University, Old Road Campus Research Building United Kingdom
Dr Brian D Marsden Structural Genomics Consortium Oxford University, Old Road Campus Research Building United Kingdom
Professor Paul Brennan Target Discovery Institute Oxford University, NDM Research Building United Kingdom
Professor Frank von Delft Structural Genomics Consortium Oxford University, Old Road Campus Research Building United Kingdom
Prof David Beeson (RDM) Weatherall Institute of Molecular Medicine Oxford University, Weatherall Institute of Molecular Medicine United Kingdom
Hresko RC, Kraft TE, Quigley A, Carpenter EP, Hruz PW. 2016. Mammalian Glucose Transporter Activity Is Dependent upon Anionic and Conical Phospholipids. J Biol Chem, 291 (33), pp. 17271-17282. | Show Abstract | Read more

The regulated movement of glucose across mammalian cell membranes is mediated by facilitative glucose transporters (GLUTs) embedded in lipid bilayers. Despite the known importance of phospholipids in regulating protein structure and activity, the lipid-induced effects on the GLUTs remain poorly understood. We systematically examined the effects of physiologically relevant phospholipids on glucose transport in liposomes containing purified GLUT4 and GLUT3. The anionic phospholipids, phosphatidic acid, phosphatidylserine, phosphatidylglycerol, and phosphatidylinositol, were found to be essential for transporter function by activating it and stabilizing its structure. Conical lipids, phosphatidylethanolamine and diacylglycerol, enhanced transporter activity up to 3-fold in the presence of anionic phospholipids but did not stabilize protein structure. Kinetic analyses revealed that both lipids increase the kcat of transport without changing the Km values. These results allowed us to elucidate the activation of GLUT by plasma membrane phospholipids and to extend the field of membrane protein-lipid interactions to the family of structurally and functionally related human solute carriers.

McClenaghan C, Schewe M, Aryal P, Carpenter EP, Baukrowitz T, Tucker SJ. 2016. Polymodal activation of the TREK-2 K2P channel produces structurally distinct open states. J Gen Physiol, 147 (6), pp. 497-505. | Show Abstract | Read more

The TREK subfamily of two-pore domain (K2P) K(+) channels exhibit polymodal gating by a wide range of physical and chemical stimuli. Crystal structures now exist for these channels in two main states referred to as the "up" and "down" conformations. However, recent studies have resulted in contradictory and mutually exclusive conclusions about the functional (i.e., conductive) status of these two conformations. To address this problem, we have used the state-dependent TREK-2 inhibitor norfluoxetine that can only bind to the down state, thereby allowing us to distinguish between these two conformations when activated by different stimuli. Our results reconcile these previously contradictory gating models by demonstrating that activation by pressure, temperature, voltage, and pH produce more than one structurally distinct open state and reveal that channel activation does not simply involve switching between the up and down conformations. These results also highlight the diversity of structural mechanisms that K2P channels use to integrate polymodal gating signals.

Pike AC, Garman EF, Krojer T, von Delft F, Carpenter EP. 2016. An overview of heavy-atom derivatization of protein crystals. Acta Crystallogr D Struct Biol, 72 (Pt 3), pp. 303-318. | Show Abstract | Read more

Heavy-atom derivatization is one of the oldest techniques for obtaining phase information for protein crystals and, although it is no longer the first choice, it remains a useful technique for obtaining phases for unknown structures and for low-resolution data sets. It is also valuable for confirming the chain trace in low-resolution electron-density maps. This overview provides a summary of the technique and is aimed at first-time users of the method. It includes guidelines on when to use it, which heavy atoms are most likely to work, how to prepare heavy-atom solutions, how to derivatize crystals and how to determine whether a crystal is in fact a derivative.

Schaedler TA, Faust B, Shintre CA, Carpenter EP, Srinivasan V, van Veen HW, Balk J. 2015. Structures and functions of mitochondrial ABC transporters. Biochem Soc Trans, 43 (5), pp. 943-951. | Show Abstract | Read more

A small number of physiologically important ATP-binding cassette (ABC) transporters are found in mitochondria. Most are half transporters of the B group forming homodimers and their topology suggests they function as exporters. The results of mutant studies point towards involvement in iron cofactor biosynthesis. In particular, ABC subfamily B member 7 (ABCB7) and its homologues in yeast and plants are required for iron-sulfur (Fe-S) cluster biosynthesis outside of the mitochondria, whereas ABCB10 is involved in haem biosynthesis. They also play a role in preventing oxidative stress. Mutations in ABCB6 and ABCB7 have been linked to human disease. Recent crystal structures of yeast Atm1 and human ABCB10 have been key to identifying substrate-binding sites and transport mechanisms. Combined with in vitro and in vivo studies, progress is being made to find the physiological substrates of the different mitochondrial ABC transporters.

Dong YY, Pike AC, Mackenzie A, McClenaghan C, Aryal P, Dong L, Quigley A, Grieben M et al. 2015. K2P channel gating mechanisms revealed by structures of TREK-2 and a complex with Prozac. Science, 347 (6227), pp. 1256-1259. | Show Abstract | Read more

TREK-2 (KCNK10/K2P10), a two-pore domain potassium (K2P) channel, is gated by multiple stimuli such as stretch, fatty acids, and pH and by several drugs. However, the mechanisms that control channel gating are unclear. Here we present crystal structures of the human TREK-2 channel (up to 3.4 angstrom resolution) in two conformations and in complex with norfluoxetine, the active metabolite of fluoxetine (Prozac) and a state-dependent blocker of TREK channels. Norfluoxetine binds within intramembrane fenestrations found in only one of these two conformations. Channel activation by arachidonic acid and mechanical stretch involves conversion between these states through movement of the pore-lining helices. These results provide an explanation for TREK channel mechanosensitivity, regulation by diverse stimuli, and possible off-target effects of the serotonin reuptake inhibitor Prozac.

Stansfeld PJ, Goose JE, Caffrey M, Carpenter EP, Parker JL, Newstead S, Sansom MS. 2015. MemProtMD: Automated Insertion of Membrane Protein Structures into Explicit Lipid Membranes. Structure, 23 (7), pp. 1350-1361. | Show Abstract | Read more

There has been exponential growth in the number of membrane protein structures determined. Nevertheless, these structures are usually resolved in the absence of their lipid environment. Coarse-grained molecular dynamics (CGMD) simulations enable insertion of membrane proteins into explicit models of lipid bilayers. We have automated the CGMD methodology, enabling membrane protein structures to be identified upon their release into the PDB and embedded into a membrane. The simulations are analyzed for protein-lipid interactions, identifying lipid binding sites, and revealing local bilayer deformations plus molecular access pathways within the membrane. The coarse-grained models of membrane protein/bilayer complexes are transformed to atomistic resolution for further analysis and simulation. Using this automated simulation pipeline, we have analyzed a number of recently determined membrane protein structures to predict their locations within a membrane, their lipid/protein interactions, and the functional implications of an enhanced understanding of the local membrane environment of each protein.

Qiu W, Liesa M, Carpenter EP, Shirihai OS. 2015. ATP Binding and Hydrolysis Properties of ABCB10 and Their Regulation by Glutathione. PLoS One, 10 (6), pp. e0129772. | Show Abstract | Read more

ABCB10 (ATP binding cassette sub-family B10) is a mitochondrial inner-membrane ABC transporter. ABCB10 has been shown to protect the heart from the impact of ROS during ischemia-reperfusion and to allow for proper hemoglobin synthesis during erythroid development. ABC transporters are proteins that increase ATP binding and hydrolysis activity in the presence of the transported substrate. However, molecular entities transported by ABCB10 and its regulatory mechanisms are currently unknown. Here we characterized ATP binding and hydrolysis properties of ABCB10 by using the 8-azido-ATP photolabeling technique. This technique can identify potential ABCB10 regulators, transported substrates and amino-acidic residues required for ATP binding and hydrolysis. We confirmed that Gly497 and Lys498 in the Walker A motif, Glu624 in the Walker B motif and Gly602 in the C-Loop motif of ABCB10 are required for proper ATP binding and hydrolysis activity, as their mutation changed ABCB10 8-Azido-ATP photo-labeling. In addition, we show that the potential ABCB10 transported entity and heme precursor delta-aminolevulinic acid (dALA) does not alter 8-azido-ATP photo-labeling. In contrast, oxidized glutathione (GSSG) stimulates ATP hydrolysis without affecting ATP binding, whereas reduced glutathione (GSH) inhibits ATP binding and hydrolysis. Indeed, we detectABCB10 glutathionylation in Cys547 and show that it is one of the exposed cysteine residues within ABCB10 structure. In all, we characterize essential residues for ABCB10 ATPase activity and we provide evidence that supports the exclusion of dALA as a potential substrate directly transported by ABCB10. Last, we show the first molecular mechanism by which mitochondrial oxidative status, through GSH/GSSG, can regulate ABCB10.

Deme JC, Hancock MA, Xia X, Shintre CA, Plesa M, Kim JC, Carpenter EP, Rosenblatt DS, Coulton JW. 2014. Purification and interaction analyses of two human lysosomal vitamin B12 transporters: LMBD1 and ABCD4. Mol Membr Biol, 31 (7-8), pp. 250-261. | Show Abstract | Read more

Mutations in human LMBRD1 and ABCD4 prevent lysosomal export of vitamin B(12) to the cytoplasm, impairing the vitamin B(12)-dependent enzymes methionine synthase and methylmalonyl-CoA mutase. The gene products of LMBRD1 and ABCD4 are implicated in vitamin B(12) transport at the lysosomal membrane and are proposed to act in complex. To address the mechanism for lysosomal vitamin B(12) transport, we report the novel recombinant production of LMBD1 and ABCD4 for detailed biophysical analyses. Using blue native PAGE, chemical crosslinking, and size exclusion chromatography coupled to multi-angle light scattering (SEC-MALS), we show that both detergent-solubilized LMBD1 and detergent-solubilized ABCD4 form homodimers. To examine the functional binding properties of these proteins, label-free surface plasmon resonance (SPR) provides direct in vitro evidence that: (i) LMBD1 and ABCD4 interact with low nanomolar affinity; and (ii) the cytoplasmic vitamin B(12)-processing protein MMACHC also interacts with LMBD1 and ABCD4 with low nanomolar affinity. Accordingly, we propose a model whereby membrane-bound LMBD1 and ABCD4 facilitate the vectorial delivery of lysosomal vitamin B(12) to cytoplasmic MMACHC, thus preventing cofactor dilution to the cytoplasmic milieu and protecting against inactivating side reactions.

Shintre CA, Pike AC, Li Q, Kim JI, Barr AJ, Goubin S, Shrestha L, Yang J et al. 2013. Structures of ABCB10, a human ATP-binding cassette transporter in apo- and nucleotide-bound states. Proc Natl Acad Sci U S A, 110 (24), pp. 9710-9715. | Show Abstract | Read more

ABCB10 is one of the three ATP-binding cassette (ABC) transporters found in the inner membrane of mitochondria. In mammals ABCB10 is essential for erythropoiesis, and for protection of mitochondria against oxidative stress. ABCB10 is therefore a potential therapeutic target for diseases in which increased mitochondrial reactive oxygen species production and oxidative stress play a major role. The crystal structure of apo-ABCB10 shows a classic exporter fold ABC transporter structure, in an open-inwards conformation, ready to bind the substrate or nucleotide from the inner mitochondrial matrix or membrane. Unexpectedly, however, ABCB10 adopts an open-inwards conformation when complexed with nonhydrolysable ATP analogs, in contrast to other transporter structures which adopt an open-outwards conformation in complex with ATP. The three complexes of ABCB10/ATP analogs reported here showed varying degrees of opening of the transport substrate binding site, indicating that in this conformation there is some flexibility between the two halves of the protein. These structures suggest that the observed plasticity, together with a portal between two helices in the transmembrane region of ABCB10, assist transport substrate entry into the substrate binding cavity. These structures indicate that ABC transporters may exist in an open-inwards conformation when nucleotide is bound. We discuss ways in which this observation can be aligned with the current views on mechanisms of ABC transporters.

Quigley A, Dong YY, Pike AC, Dong L, Shrestha L, Berridge G, Stansfeld PJ, Sansom MS et al. 2013. The structural basis of ZMPSTE24-dependent laminopathies. Science, 339 (6127), pp. 1604-1607. | Show Abstract | Read more

Mutations in the nuclear membrane zinc metalloprotease ZMPSTE24 lead to diseases of lamin processing (laminopathies), such as the premature aging disease progeria and metabolic disorders. ZMPSTE24 processes prelamin A, a component of the nuclear lamina intermediate filaments, by cleaving it at two sites. Failure of this processing results in accumulation of farnesylated, membrane-associated prelamin A. The 3.4 angstrom crystal structure of human ZMPSTE24 has a seven transmembrane α-helical barrel structure, surrounding a large, water-filled, intramembrane chamber, capped by a zinc metalloprotease domain with the catalytic site facing into the chamber. The 3.8 angstrom structure of a complex with a CSIM tetrapeptide showed that the mode of binding of the substrate resembles that of an insect metalloprotease inhibitor in thermolysin. Laminopathy-associated mutations predicted to reduce ZMPSTE24 activity map to the zinc metalloprotease peptide-binding site and to the bottom of the chamber.

Lu D, Silhan J, MacDonald JT, Carpenter EP, Jensen K, Tang CM, Baldwin GS, Freemont PS. 2012. Structural basis for the recognition and cleavage of abasic DNA in Neisseria meningitidis. Proc Natl Acad Sci U S A, 109 (42), pp. 16852-16857. | Show Abstract | Read more

Base excision repair (BER) is a highly conserved DNA repair pathway throughout all kingdoms from bacteria to humans. Whereas several enzymes are required to complete the multistep repair process of damaged bases, apurinic-apyrimidic (AP) endonucleases play an essential role in enabling the repair process by recognizing intermediary abasic sites cleaving the phosphodiester backbone 5' to the abasic site. Despite extensive study, there is no structure of a bacterial AP endonuclease bound to substrate DNA. Furthermore, the structural mechanism for AP-site cleavage is incomplete. Here we report a detailed structural and biochemical study of the AP endonuclease from Neisseria meningitidis that has allowed us to capture structural intermediates providing more complete snapshots of the catalytic mechanism. Our data reveal subtle differences in AP-site recognition and kinetics between the human and bacterial enzymes that may reflect different evolutionary pressures.

Bailey D, Carpenter EP, Coker A, Coker S, Read J, Jones AT, Erskine P, Aguilar CF et al. 2012. An analysis of subdomain orientation, conformational change and disorder in relation to crystal packing of aspartic proteinases. Acta Crystallogr D Biol Crystallogr, 68 (Pt 5), pp. 541-552. | Show Abstract | Read more

The analysis reported here describes detailed structural studies of endothiapepsin (the aspartic proteinase from Endothia parasitica), with and without bound inhibitors, and human pepsin 3b. Comparison of multiple crystal structures of members of the aspartic proteinase family has revealed small but significant differences in domain orientation in different crystal forms. In this paper, it is shown that these differences in domain orientation do not necessarily correlate with the presence or absence of bound inhibitors, but appear to stem at least partly from crystal contacts mediated by sulfate ions. However, since the same inherent flexibility of the structure is observed for other enzymes in this family such as human pepsin, the native structure of which is also reported here, the observed domain movements may well have implications for the mechanism of catalysis.

Berridge G, Chalk R, D'Avanzo N, Dong L, Doyle D, Kim JI, Xia X, Burgess-Brown N, Deriso A, Carpenter EP, Gileadi O. 2011. High-performance liquid chromatography separation and intact mass analysis of detergent-solubilized integral membrane proteins Analytical Biochemistry, 410 (2), pp. 272-280. | Show Abstract | Read more

We have developed a method for intact mass analysis of detergent- solubilized and purified integral membrane proteins using liquid chromatography-mass spectrometry (LC-MS) with methanol as the organic mobile phase. Membrane proteins and detergents are separated chromatographically during the isocratic stage of the gradient profile from a 150-mm C3 reversed-phase column. The mass accuracy is comparable to standard methods employed for soluble proteins; the sensitivity is 10-fold lower, requiring 0.2-5 μg of protein. The method is also compatible with our standard LC-MS method used for intact mass analysis of soluble proteins and may therefore be applied on a multiuser instrument or in a high-throughput environment. © 2010 Elsevier Inc. All rights reserved.

Cited:

122

Scopus

Newstead S, Drew D, Cameron AD, Postis VLG, Xia X, Fowler PW, Ingram JC, Carpenter EP et al. 2011. Crystal structure of a prokaryotic homologue of the mammalian oligopeptide-proton symporters, PepT1 and PepT2 EMBO Journal, 30 (2), pp. 417-426. | Show Abstract | Read more

PepT1 and PepT2 are major facilitator superfamily (MFS) transporters that utilize a proton gradient to drive the uptake of di- and tri-peptides in the small intestine and kidney, respectively. They are the major routes by which we absorb dietary nitrogen and many orally administered drugs. Here, we present the crystal structure of PepT So, a functionally similar prokaryotic homologue of the mammalian peptide transporters from Shewanella oneidensis. This structure, refined using data up to 3.6 Å resolution, reveals a ligand-bound occluded state for the MFS and provides new insights into a general transport mechanism. We have located the peptide-binding site in a central hydrophilic cavity, which occludes a bound ligand from both sides of the membrane. Residues thought to be involved in proton coupling have also been identified near the extracellular gate of the cavity. Based on these findings and associated kinetic data, we propose that PepT So represents a sound model system for understanding mammalian peptide transport as catalysed by PepT1 and PepT2. © 2011 European Molecular Biology Organization | All Rights Reserved.

Newstead S, Drew D, Cameron AD, Postis VL, Xia X, Fowler PW, Ingram JC, Carpenter EP et al. 2011. Crystal structure of a prokaryotic homologue of the mammalian oligopeptide-proton symporters, PepT1 and PepT2. EMBO J, 30 (2), pp. 417-426. | Show Abstract | Read more

PepT1 and PepT2 are major facilitator superfamily (MFS) transporters that utilize a proton gradient to drive the uptake of di- and tri-peptides in the small intestine and kidney, respectively. They are the major routes by which we absorb dietary nitrogen and many orally administered drugs. Here, we present the crystal structure of PepT(So), a functionally similar prokaryotic homologue of the mammalian peptide transporters from Shewanella oneidensis. This structure, refined using data up to 3.6 Å resolution, reveals a ligand-bound occluded state for the MFS and provides new insights into a general transport mechanism. We have located the peptide-binding site in a central hydrophilic cavity, which occludes a bound ligand from both sides of the membrane. Residues thought to be involved in proton coupling have also been identified near the extracellular gate of the cavity. Based on these findings and associated kinetic data, we propose that PepT(So) represents a sound model system for understanding mammalian peptide transport as catalysed by PepT1 and PepT2.

Berridge G, Chalk R, D'Avanzo N, Dong L, Doyle D, Kim JI, Xia X, Burgess-Brown N, Deriso A, Carpenter EP, Gileadi O. 2011. High-performance liquid chromatography separation and intact mass analysis of detergent-solubilized integral membrane proteins. Anal Biochem, 410 (2), pp. 272-280. | Show Abstract | Read more

We have developed a method for intact mass analysis of detergent-solubilized and purified integral membrane proteins using liquid chromatography-mass spectrometry (LC-MS) with methanol as the organic mobile phase. Membrane proteins and detergents are separated chromatographically during the isocratic stage of the gradient profile from a 150-mm C3 reversed-phase column. The mass accuracy is comparable to standard methods employed for soluble proteins; the sensitivity is 10-fold lower, requiring 0.2-5 μg of protein. The method is also compatible with our standard LC-MS method used for intact mass analysis of soluble proteins and may therefore be applied on a multiuser instrument or in a high-throughput environment.

Albesa-Jové D, Bertrand T, Carpenter EP, Swain GV, Lim J, Zhang J, Haire LF, Vasisht N et al. 2010. Four distinct structural domains in Clostridium difficile toxin B visualized using SAXS. J Mol Biol, 396 (5), pp. 1260-1270. | Show Abstract | Read more

Clostridium difficile is a nosocomial bacterial pathogen causing antibiotic-associated diarrhea and fatal pseudomembranous colitis. Key virulence factors are toxin A and toxin B (TcdB), two highly related toxins that are members of the large clostridial toxin family. These large multifunctional proteins disrupt cell function using a glucosyltransferase domain that is translocated into the cytosol after vesicular internalization of intact holotoxin. Although substantial information about the biochemical mechanisms of intoxication exists, research has been hampered by limited structural information, particularly of intact holotoxin. Here, we used small-angle X-ray scattering (SAXS) methods to obtain an ab initio low-resolution structure of native TcdB, which demonstrated that this molecule is monomeric in solution and possesses a highly asymmetric shape with a maximum dimension of approximately 275 A. Combining this SAXS information with crystallographic or modeled structures of individual functional domains of TcdB reveals for the first time that the three-dimensional structure of TcdB is organized into four distinct structural domains. Structures of the N-terminal glucosyltransferase, the cysteine protease, and the C-terminal repeat region can be aligned within three domains of the SAXS envelope. A fourth domain, predicted to be involved in the translocation of the glucosyltransferase, appears as a large solvent-exposed protrusion. Knowledge of the shapes and relative orientations of toxin domains provides new insight into defining functional domain boundaries and provides a framework for understanding how potential intra-domain interactions enable conformational changes to propagate between domains to facilitate intoxication processes.

Newstead S, Fowler PW, Bilton P, Carpenter EP, Sadler PJ, Campopiano DJ, Sansom MS, Iwata S. 2009. Insights into how nucleotide-binding domains power ABC transport. Structure, 17 (9), pp. 1213-1222. | Show Abstract | Read more

The mechanism by which nucleotide-binding domains (NBDs) of ABC transporters power the transport of substrates across cell membranes is currently unclear. Here we report the crystal structure of an NBD, FbpC, from the Neisseria gonorrhoeae ferric iron uptake transporter with an unusual and substantial domain swap in the C-terminal regulatory domain. This entanglement suggests that FbpC is unable to open to the same extent as the homologous protein MalK. Using molecular dynamics we demonstrate that this is not the case: both NBDs open rapidly once ATP is removed. We conclude from this result that the closed structures of FbpC and MalK have higher free energies than their respective open states. This result has important implications for our understanding of the mechanism of power generation in ABC transporters, because the unwinding of this free energy ensures that the opening of these two NBDs is also powered.

Andréll J, Hicks MG, Palmer T, Carpenter EP, Iwata S, Maher MJ. 2009. Crystal structure of the acid-induced arginine decarboxylase from Escherichia coli: reversible decamer assembly controls enzyme activity. Biochemistry, 48 (18), pp. 3915-3927. | Show Abstract | Read more

The acid-induced arginine decarboxylase is part of an enzymatic system in Escherichia coli that contributes to making this organism acid resistant. The arginine decarboxylase is a vitamin B(6)-dependent enzyme that is active at acidic pH. It consumes a proton in the decarboxylation of arginine to agmatine, and by working in tandem with an arginine-agmatine antiporter, this enzymatic cycle protects the organism by preventing the accumulation of protons inside the cell. We have determined the structure of the acid-induced arginine decarboxylase by X-ray crystallography to 2.4 A resolution. The arginine decarboxylase structure revealed a ca. 800 kDa decamer composed as a pentamer of five homodimers. Each homodimer has an abundance of acidic surface residues, which at neutral pH prevents inactive homodimers from associating into active decamers. Conversely, acidic conditions favor the assembly of active decamers. Therefore, the structure of arginine decarboxylase presents a mechanism by which its activity is modulated by external pH.

Newstead S, Hobbs J, Jordan D, Carpenter EP, Iwata S. 2008. Insights into outer membrane protein crystallization. Mol Membr Biol, 25 (8), pp. 631-638. | Show Abstract | Read more

Outer membrane proteins are structurally distinct from those that reside in the inner membrane and play important roles in bacterial pathogenicity and human metabolism. X-ray crystallography studies on >40 different outer membrane proteins have revealed that the transmembrane portion of these proteins can be constructed from either beta-sheets or less commonly from alpha-helices. The most common architecture is the beta-barrel, which can be formed from either a single anti-parallel sheet, fused at both ends to form a barrel or from multiple peptide chains. Outer membrane proteins exhibit considerable rigidity and stability, making their study through x-ray crystallography particularly tractable. As the number of structures of outer membrane proteins increases a more rational approach to their crystallization can be made. Herein we analyse the crystallization data from 53 outer membrane proteins and compare the results to those obtained for inner membrane proteins. A targeted sparse matrix screen for outer membrane protein crystallization is presented based on the present analysis.

Weyand S, Shimamura T, Yajima S, Suzuki S, Mirza O, Krusong K, Carpenter EP, Rutherford NG et al. 2008. Structure and molecular mechanism of a nucleobase-cation-symport-1 family transporter. Science, 322 (5902), pp. 709-713. | Show Abstract | Read more

The nucleobase-cation-symport-1 (NCS1) transporters are essential components of salvage pathways for nucleobases and related metabolites. Here, we report the 2.85-angstrom resolution structure of the NCS1 benzyl-hydantoin transporter, Mhp1, from Microbacterium liquefaciens. Mhp1 contains 12 transmembrane helices, 10 of which are arranged in two inverted repeats of five helices. The structures of the outward-facing open and substrate-bound occluded conformations were solved, showing how the outward-facing cavity closes upon binding of substrate. Comparisons with the leucine transporter LeuT(Aa) and the galactose transporter vSGLT reveal that the outward- and inward-facing cavities are symmetrically arranged on opposite sides of the membrane. The reciprocal opening and closing of these cavities is synchronized by the inverted repeat helices 3 and 8, providing the structural basis of the alternating access model for membrane transport.

Carpenter EP, Beis K, Cameron AD, Iwata S. 2008. Overcoming the challenges of membrane protein crystallography. Curr Opin Struct Biol, 18 (5), pp. 581-586. | Show Abstract | Read more

Membrane protein structural biology is still a largely unconquered area, given that approximately 25% of all proteins are membrane proteins and yet less than 150 unique structures are available. Membrane proteins have proven to be difficult to study owing to their partially hydrophobic surfaces, flexibility and lack of stability. The field is now taking advantage of the high-throughput revolution in structural biology and methods are emerging for effective expression, solubilisation, purification and crystallisation of membrane proteins. These technical advances will lead to a rapid increase in the rate at which membrane protein structures are solved in the near future.

Kouwen TR, Andréll J, Schrijver R, Dubois JY, Maher MJ, Iwata S, Carpenter EP, van Dijl JM. 2008. Thioredoxin A active-site mutants form mixed disulfide dimers that resemble enzyme-substrate reaction intermediates. J Mol Biol, 379 (3), pp. 520-534. | Show Abstract | Read more

Thioredoxin functions in nearly all organisms as the major thiol-disulfide oxidoreductase within the cytosol. Its prime purpose is to maintain cysteine-containing proteins in the reduced state by converting intramolecular disulfide bonds into dithiols in a disulfide exchange reaction. Thioredoxin has been reported to contribute to a wide variety of physiological functions by interacting with specific sets of substrates in different cell types. To investigate the function of the essential thioredoxin A (TrxA) in the low-GC Gram-positive bacterium Bacillus subtilis, we purified wild-type TrxA and three mutant TrxA proteins that lack either one or both of the two cysteine residues in the CxxC active site. The pure proteins were used for substrate-binding studies known as "mixed disulfide fishing" in which covalent disulfide-bonded reaction intermediates can be visualized. An unprecedented finding is that both active-site cysteine residues can form mixed disulfides with substrate proteins when the other active-site cysteine is absent, but only the N-terminal active-site cysteine forms stable interactions. A second novelty is that both single-cysteine mutant TrxA proteins form stable homodimers due to thiol oxidation of the remaining active-site cysteine residue. To investigate whether these dimers resemble mixed enzyme-substrate disulfides, the structure of the most abundant dimer, C32S, was characterized by X-ray crystallography. This yielded a high-resolution (1.5A) X-ray crystallographic structure of a thioredoxin homodimer from a low-GC Gram-positive bacterium. The C32S TrxA dimer can be regarded as a mixed disulfide reaction intermediate of thioredoxin, which reveals the diversity of thioredoxin/substrate-binding modes.

Blumenschein TM, Friedrich N, Childs RA, Saouros S, Carpenter EP, Campanero-Rhodes MA, Simpson P, Chai W et al. 2007. Atomic resolution insight into host cell recognition by Toxoplasma gondii. EMBO J, 26 (11), pp. 2808-2820. | Show Abstract | Read more

The obligate intracellular parasite Toxoplasma gondii, a member of the phylum Apicomplexa that includes Plasmodium spp., is one of the most widespread parasites and the causative agent of toxoplasmosis. Micronemal proteins (MICs) are released onto the parasite surface just before invasion of host cells and play important roles in host cell recognition, attachment and penetration. Here, we report the atomic structure for a key MIC, TgMIC1, and reveal a novel cell-binding motif called the microneme adhesive repeat (MAR). Using glycoarray analyses, we identified a novel interaction with sialylated oligosaccharides that resolves several prevailing misconceptions concerning TgMIC1. Structural studies of various complexes between TgMIC1 and sialylated oligosaccharides provide high-resolution insights into the recognition of sialylated oligosaccharides by a parasite surface protein. We observe that MAR domains exist in tandem repeats, which provide a highly specialized structure for glycan discrimination. Our work uncovers new features of parasite-receptor interactions at the early stages of host cell invasion, which will assist the design of new therapeutic strategies.

Carpenter EP, Corbett A, Thomson H, Adacha J, Jensen K, Bergeron J, Kasampalidis I, Exley R et al. 2007. AP endonuclease paralogues with distinct activities in DNA repair and bacterial pathogenesis. EMBO J, 26 (5), pp. 1363-1372. | Show Abstract | Read more

Oxidative stress is a principal cause of DNA damage, and mechanisms to repair this damage are among the most highly conserved of biological processes. Oxidative stress is also used by phagocytes to attack bacterial pathogens in defence of the host. We have identified and characterised two apurinic/apyrimidinic (AP) endonuclease paralogues in the human pathogen Neisseria meningitidis. The presence of multiple versions of DNA repair enzymes in a single organism is usually thought to reflect redundancy in activities that are essential for cellular viability. We demonstrate here that these two AP endonuclease paralogues have distinct activities in DNA repair: one is a typical Neisserial AP endonuclease (NApe), whereas the other is a specialised 3'-phosphodiesterase Neisserial exonuclease (NExo). The lack of AP endonuclease activity of NExo is shown to be attributable to the presence of a histidine side chain, blocking the abasic ribose-binding site. Both enzymes are necessary for survival of N. meningitidis under oxidative stress and during bloodstream infection. The novel functional pairing of NExo and NApe is widespread among bacteria and appears to have evolved independently on several occasions.

Saouros S, Blumenschein TM, Sawmynaden K, Marchant J, Koutroukides T, Liu B, Simpson P, Carpenter EP, Matthews SJ. 2007. High-level bacterial expression and purification of apicomplexan micronemal proteins for structural studies. Protein Pept Lett, 14 (5), pp. 411-415. | Show Abstract | Read more

The cysteine-rich N-terminal domain of the micronemal adhesive protein MIC1 (MIC1-NT) from Toxoplasma gondii was cloned, expressed in Escherichia coli and purified. MIC1-NT is amenable to structural studies as shown by preliminary NMR and X-ray analysis. Positive results with two further micronemal proteins indicate that our strategy has wider application.

Krusong K, Carpenter EP, Bellamy SR, Savva R, Baldwin GS. 2006. A comparative study of uracil-DNA glycosylases from human and herpes simplex virus type 1. J Biol Chem, 281 (8), pp. 4983-4992. | Show Abstract | Read more

Uracil-DNA glycosylase (UNG) is the key enzyme responsible for initiation of base excision repair. We have used both kinetic and binding assays for comparative analysis of UNG enzymes from humans and herpes simplex virus type 1 (HSV-1). Steady-state fluorescence assays showed that hUNG has a much higher specificity constant (k(cat)/K(m)) compared with the viral enzyme due to a lower K(m). The binding of UNG to DNA was also studied using a catalytically inactive mutant of UNG and non-cleavable substrate analogs (2'-deoxypseudouridine and 2'-alpha-fluoro-2'-deoxyuridine). Equilibrium DNA binding revealed that both human and HSV-1 UNG enzymes bind to abasic DNA and both substrate analogs more weakly than to uracil-containing DNA. Structure determination of HSV-1 D88N/H210N UNG in complex with uracil revealed detailed information on substrate binding. Together, these results suggest that a significant proportion of the binding energy is provided by specific interactions with the target uracil. The kinetic parameters for human UNG indicate that it is likely to have activity against both U.A and U.G mismatches in vivo. Weak binding to abasic DNA also suggests that UNG activity is unlikely to be coupled to the subsequent common steps of base excision repair.

Makyio H, Iino R, Ikeda C, Imamura H, Tamakoshi M, Iwata M, Stock D, Bernal RA et al. 2005. Structure of a central stalk subunit F of prokaryotic V-type ATPase/synthase from Thermus thermophilus. EMBO J, 24 (22), pp. 3974-3983. | Show Abstract | Read more

The crystal structure of subunit F of vacuole-type ATPase/synthase (prokaryotic V-ATPase) was determined to of 2.2 A resolution. The subunit reveals unexpected structural similarity to the response regulator proteins that include the Escherichia coli chemotaxis response regulator CheY. The structure was successfully placed into the low-resolution EM structure of the prokaryotic holo-V-ATPase at a location indicated by the results of crosslinking experiments. The crystal structure, together with the single-molecule analysis using fluorescence resonance energy transfer, showed that the subunit F exhibits two conformations, a 'retracted' form in the absence and an 'extended' form in the presence of ATP. Our results postulated that the subunit F is a regulatory subunit in the V-ATPase.

Brown KA, Carpenter EP, Watson KA, Coggins JR, Hawkins AR, Koch MH, Svergun DI. 2003. Twists and turns: a tale of two shikimate-pathway enzymes. Biochem Soc Trans, 31 (Pt 3), pp. 543-547. | Show Abstract | Read more

We are studying two enzymes from the shikimate pathway, dehydroquinate synthase (DHQS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Both enzymes have been the subject of numerous studies to elucidate their reaction mechanisms. Crystal structures of DHQS and EPSPS in the presence and absence of substrates, cofactors and/or inhibitors are now available. These structures reveal movements of domains, rearrangements of loops and changes in side-chain positions necessary for the formation of a catalytically competent active site. The potential for using complementary small-angle X-ray scattering (SAXS) studies to confirm the presence of these structural differences in solution has also been explored. Comparative analysis of crystal structures, in the presence and absence of ligands, has revealed structural features critical for substrate-binding and catalysis. We have also analysed these structures by generating GRID energy maps to detect favourable binding sites. The combination of X-ray crystallography, SAXS and computational techniques provides an enhanced analysis of structural features important for the function of these complex enzymes.

Gelb MH, Van Voorhis WC, Buckner FS, Yokoyama K, Eastman R, Carpenter EP, Panethymitaki C, Brown KA, Smith DF. 2003. Protein farnesyl and N-myristoyl transferases: piggy-back medicinal chemistry targets for the development of antitrypanosomatid and antimalarial therapeutics. Mol Biochem Parasitol, 126 (2), pp. 155-163. | Show Abstract | Read more

To accelerate progress in the development of therapeutics for protozoan parasitic diseases, we are studying enzymes active in co- and post-translational protein modification that are already the focus of drug development in other eukaryotic systems. Inhibitors of the protein farnesyltransferases (PFT) are well-established antitumour agents of low cytotoxicity and known pharmokinetic properties, while inhibitors of N-myristoyl transferase show both selectivity and specificity in the treatment of fungal infections. Here, we summarise the current evidence that supports the targeting of these ubiquitous eukaryotic enzymes for drug development against trypanosomatid infections and malaria.

Brown KA, Carpenter EP. 2000. Multistep catalysis dehydroquinate synthase. FASEB JOURNAL, 14 (8), pp. A1583-A1583.

Withers-Martinez C, Carpenter EP, Hackett F, Ely B, Sajid M, Grainger M, Blackman MJ. 1999. PCR-based gene synthesis as an efficient approach for expression of the A+T-rich malaria genome. Protein Eng, 12 (12), pp. 1113-1120. | Show Abstract | Read more

The A+T-rich genome of the human malaria parasite Plasmodium falciparum encodes genes of biological importance that cannot be expressed efficiently in heterologous eukaryotic systems, owing to an extremely biased codon usage and the presence of numerous cryptic polyadenylation sites. In this work we have optimized an assembly polymerase chain reaction (PCR) method for the fast and extremely accurate synthesis of a 2.1 kb Plasmodium falciparum gene (pfsub-1) encoding a subtilisin-like protease. A total of 104 oligonucleotides, designed with the aid of dedicated computer software, were assembled in a single-step PCR. The assembly was then further amplified by PCR to produce a synthetic gene which has been cloned and successfully expressed in both Pichia pastoris and recombinant baculovirus-infected High Five(TM) cells. We believe this strategy to be of special interest as it is simple, accessible and has no limitation with respect to the size of the gene to be synthesized. Used as a systematic approach for the malarial genome or any other A + T-rich organism, the method allows the rapid synthesis of a nucleotide sequence optimized for expression in the system of choice and production of sufficiently large amounts of biological material for complete molecular and structural characterization.

Carpenter EP, Hawkins AR, Frost JW, Brown KA. 1998. Structure of dehydroquinate synthase reveals an active site capable of multistep catalysis. Nature, 394 (6690), pp. 299-302. | Show Abstract | Read more

Dehydroquinate synthase (DHQS) has long been regarded as a catalytic marvel because of its ability to perform several consecutive chemical reactions in one active site. There has been considerable debate as to whether DHQS is actively involved in all these steps, or whether several steps occur spontaneously, making DHQS a spectator in its own mechanism. DHQS performs the second step in the shikimate pathway, which is required for the synthesis of aromatic compounds in bacteria, microbial eukaryotes and plants. This enzyme is a potential target for new antifungal and antibacterial drugs as the shikimate pathway is absent from mammals and DHQS is required for pathogen virulence. Here we report the crystal structure of DHQS, which has several unexpected features, including a previously unobserved mode for NAD+-binding and an active-site organization that is surprisingly similar to that of alcohol dehydrogenase, in a new protein fold. The structure reveals interactions between the active site and a substrate-analogue inhibitor, which indicate how DHQS can perform multistep catalysis without the formation of unwanted by-products.

McClenaghan C, Schewe M, Aryal P, Carpenter EP, Baukrowitz T, Tucker SJ. 2016. Polymodal activation of the TREK-2 K2P channel produces structurally distinct open states. J Gen Physiol, 147 (6), pp. 497-505. | Show Abstract | Read more

The TREK subfamily of two-pore domain (K2P) K(+) channels exhibit polymodal gating by a wide range of physical and chemical stimuli. Crystal structures now exist for these channels in two main states referred to as the "up" and "down" conformations. However, recent studies have resulted in contradictory and mutually exclusive conclusions about the functional (i.e., conductive) status of these two conformations. To address this problem, we have used the state-dependent TREK-2 inhibitor norfluoxetine that can only bind to the down state, thereby allowing us to distinguish between these two conformations when activated by different stimuli. Our results reconcile these previously contradictory gating models by demonstrating that activation by pressure, temperature, voltage, and pH produce more than one structurally distinct open state and reveal that channel activation does not simply involve switching between the up and down conformations. These results also highlight the diversity of structural mechanisms that K2P channels use to integrate polymodal gating signals.

Pike AC, Garman EF, Krojer T, von Delft F, Carpenter EP. 2016. An overview of heavy-atom derivatization of protein crystals. Acta Crystallogr D Struct Biol, 72 (Pt 3), pp. 303-318. | Show Abstract | Read more

Heavy-atom derivatization is one of the oldest techniques for obtaining phase information for protein crystals and, although it is no longer the first choice, it remains a useful technique for obtaining phases for unknown structures and for low-resolution data sets. It is also valuable for confirming the chain trace in low-resolution electron-density maps. This overview provides a summary of the technique and is aimed at first-time users of the method. It includes guidelines on when to use it, which heavy atoms are most likely to work, how to prepare heavy-atom solutions, how to derivatize crystals and how to determine whether a crystal is in fact a derivative.

Dong YY, Pike AC, Mackenzie A, McClenaghan C, Aryal P, Dong L, Quigley A, Grieben M et al. 2015. K2P channel gating mechanisms revealed by structures of TREK-2 and a complex with Prozac. Science, 347 (6227), pp. 1256-1259. | Show Abstract | Read more

TREK-2 (KCNK10/K2P10), a two-pore domain potassium (K2P) channel, is gated by multiple stimuli such as stretch, fatty acids, and pH and by several drugs. However, the mechanisms that control channel gating are unclear. Here we present crystal structures of the human TREK-2 channel (up to 3.4 angstrom resolution) in two conformations and in complex with norfluoxetine, the active metabolite of fluoxetine (Prozac) and a state-dependent blocker of TREK channels. Norfluoxetine binds within intramembrane fenestrations found in only one of these two conformations. Channel activation by arachidonic acid and mechanical stretch involves conversion between these states through movement of the pore-lining helices. These results provide an explanation for TREK channel mechanosensitivity, regulation by diverse stimuli, and possible off-target effects of the serotonin reuptake inhibitor Prozac.

Stansfeld PJ, Goose JE, Caffrey M, Carpenter EP, Parker JL, Newstead S, Sansom MS. 2015. MemProtMD: Automated Insertion of Membrane Protein Structures into Explicit Lipid Membranes. Structure, 23 (7), pp. 1350-1361. | Show Abstract | Read more

There has been exponential growth in the number of membrane protein structures determined. Nevertheless, these structures are usually resolved in the absence of their lipid environment. Coarse-grained molecular dynamics (CGMD) simulations enable insertion of membrane proteins into explicit models of lipid bilayers. We have automated the CGMD methodology, enabling membrane protein structures to be identified upon their release into the PDB and embedded into a membrane. The simulations are analyzed for protein-lipid interactions, identifying lipid binding sites, and revealing local bilayer deformations plus molecular access pathways within the membrane. The coarse-grained models of membrane protein/bilayer complexes are transformed to atomistic resolution for further analysis and simulation. Using this automated simulation pipeline, we have analyzed a number of recently determined membrane protein structures to predict their locations within a membrane, their lipid/protein interactions, and the functional implications of an enhanced understanding of the local membrane environment of each protein.

Qiu W, Liesa M, Carpenter EP, Shirihai OS. 2015. ATP Binding and Hydrolysis Properties of ABCB10 and Their Regulation by Glutathione. PLoS One, 10 (6), pp. e0129772. | Show Abstract | Read more

ABCB10 (ATP binding cassette sub-family B10) is a mitochondrial inner-membrane ABC transporter. ABCB10 has been shown to protect the heart from the impact of ROS during ischemia-reperfusion and to allow for proper hemoglobin synthesis during erythroid development. ABC transporters are proteins that increase ATP binding and hydrolysis activity in the presence of the transported substrate. However, molecular entities transported by ABCB10 and its regulatory mechanisms are currently unknown. Here we characterized ATP binding and hydrolysis properties of ABCB10 by using the 8-azido-ATP photolabeling technique. This technique can identify potential ABCB10 regulators, transported substrates and amino-acidic residues required for ATP binding and hydrolysis. We confirmed that Gly497 and Lys498 in the Walker A motif, Glu624 in the Walker B motif and Gly602 in the C-Loop motif of ABCB10 are required for proper ATP binding and hydrolysis activity, as their mutation changed ABCB10 8-Azido-ATP photo-labeling. In addition, we show that the potential ABCB10 transported entity and heme precursor delta-aminolevulinic acid (dALA) does not alter 8-azido-ATP photo-labeling. In contrast, oxidized glutathione (GSSG) stimulates ATP hydrolysis without affecting ATP binding, whereas reduced glutathione (GSH) inhibits ATP binding and hydrolysis. Indeed, we detectABCB10 glutathionylation in Cys547 and show that it is one of the exposed cysteine residues within ABCB10 structure. In all, we characterize essential residues for ABCB10 ATPase activity and we provide evidence that supports the exclusion of dALA as a potential substrate directly transported by ABCB10. Last, we show the first molecular mechanism by which mitochondrial oxidative status, through GSH/GSSG, can regulate ABCB10.

Deme JC, Hancock MA, Xia X, Shintre CA, Plesa M, Kim JC, Carpenter EP, Rosenblatt DS, Coulton JW. 2014. Purification and interaction analyses of two human lysosomal vitamin B12 transporters: LMBD1 and ABCD4. Mol Membr Biol, 31 (7-8), pp. 250-261. | Show Abstract | Read more

Mutations in human LMBRD1 and ABCD4 prevent lysosomal export of vitamin B(12) to the cytoplasm, impairing the vitamin B(12)-dependent enzymes methionine synthase and methylmalonyl-CoA mutase. The gene products of LMBRD1 and ABCD4 are implicated in vitamin B(12) transport at the lysosomal membrane and are proposed to act in complex. To address the mechanism for lysosomal vitamin B(12) transport, we report the novel recombinant production of LMBD1 and ABCD4 for detailed biophysical analyses. Using blue native PAGE, chemical crosslinking, and size exclusion chromatography coupled to multi-angle light scattering (SEC-MALS), we show that both detergent-solubilized LMBD1 and detergent-solubilized ABCD4 form homodimers. To examine the functional binding properties of these proteins, label-free surface plasmon resonance (SPR) provides direct in vitro evidence that: (i) LMBD1 and ABCD4 interact with low nanomolar affinity; and (ii) the cytoplasmic vitamin B(12)-processing protein MMACHC also interacts with LMBD1 and ABCD4 with low nanomolar affinity. Accordingly, we propose a model whereby membrane-bound LMBD1 and ABCD4 facilitate the vectorial delivery of lysosomal vitamin B(12) to cytoplasmic MMACHC, thus preventing cofactor dilution to the cytoplasmic milieu and protecting against inactivating side reactions.

Shintre CA, Pike AC, Li Q, Kim JI, Barr AJ, Goubin S, Shrestha L, Yang J et al. 2013. Structures of ABCB10, a human ATP-binding cassette transporter in apo- and nucleotide-bound states. Proc Natl Acad Sci U S A, 110 (24), pp. 9710-9715. | Show Abstract | Read more

ABCB10 is one of the three ATP-binding cassette (ABC) transporters found in the inner membrane of mitochondria. In mammals ABCB10 is essential for erythropoiesis, and for protection of mitochondria against oxidative stress. ABCB10 is therefore a potential therapeutic target for diseases in which increased mitochondrial reactive oxygen species production and oxidative stress play a major role. The crystal structure of apo-ABCB10 shows a classic exporter fold ABC transporter structure, in an open-inwards conformation, ready to bind the substrate or nucleotide from the inner mitochondrial matrix or membrane. Unexpectedly, however, ABCB10 adopts an open-inwards conformation when complexed with nonhydrolysable ATP analogs, in contrast to other transporter structures which adopt an open-outwards conformation in complex with ATP. The three complexes of ABCB10/ATP analogs reported here showed varying degrees of opening of the transport substrate binding site, indicating that in this conformation there is some flexibility between the two halves of the protein. These structures suggest that the observed plasticity, together with a portal between two helices in the transmembrane region of ABCB10, assist transport substrate entry into the substrate binding cavity. These structures indicate that ABC transporters may exist in an open-inwards conformation when nucleotide is bound. We discuss ways in which this observation can be aligned with the current views on mechanisms of ABC transporters.

Quigley A, Dong YY, Pike AC, Dong L, Shrestha L, Berridge G, Stansfeld PJ, Sansom MS et al. 2013. The structural basis of ZMPSTE24-dependent laminopathies. Science, 339 (6127), pp. 1604-1607. | Show Abstract | Read more

Mutations in the nuclear membrane zinc metalloprotease ZMPSTE24 lead to diseases of lamin processing (laminopathies), such as the premature aging disease progeria and metabolic disorders. ZMPSTE24 processes prelamin A, a component of the nuclear lamina intermediate filaments, by cleaving it at two sites. Failure of this processing results in accumulation of farnesylated, membrane-associated prelamin A. The 3.4 angstrom crystal structure of human ZMPSTE24 has a seven transmembrane α-helical barrel structure, surrounding a large, water-filled, intramembrane chamber, capped by a zinc metalloprotease domain with the catalytic site facing into the chamber. The 3.8 angstrom structure of a complex with a CSIM tetrapeptide showed that the mode of binding of the substrate resembles that of an insect metalloprotease inhibitor in thermolysin. Laminopathy-associated mutations predicted to reduce ZMPSTE24 activity map to the zinc metalloprotease peptide-binding site and to the bottom of the chamber.

Lu D, Silhan J, MacDonald JT, Carpenter EP, Jensen K, Tang CM, Baldwin GS, Freemont PS. 2012. Structural basis for the recognition and cleavage of abasic DNA in Neisseria meningitidis. Proc Natl Acad Sci U S A, 109 (42), pp. 16852-16857. | Show Abstract | Read more

Base excision repair (BER) is a highly conserved DNA repair pathway throughout all kingdoms from bacteria to humans. Whereas several enzymes are required to complete the multistep repair process of damaged bases, apurinic-apyrimidic (AP) endonucleases play an essential role in enabling the repair process by recognizing intermediary abasic sites cleaving the phosphodiester backbone 5' to the abasic site. Despite extensive study, there is no structure of a bacterial AP endonuclease bound to substrate DNA. Furthermore, the structural mechanism for AP-site cleavage is incomplete. Here we report a detailed structural and biochemical study of the AP endonuclease from Neisseria meningitidis that has allowed us to capture structural intermediates providing more complete snapshots of the catalytic mechanism. Our data reveal subtle differences in AP-site recognition and kinetics between the human and bacterial enzymes that may reflect different evolutionary pressures.

Bailey D, Carpenter EP, Coker A, Coker S, Read J, Jones AT, Erskine P, Aguilar CF et al. 2012. An analysis of subdomain orientation, conformational change and disorder in relation to crystal packing of aspartic proteinases. Acta Crystallogr D Biol Crystallogr, 68 (Pt 5), pp. 541-552. | Show Abstract | Read more

The analysis reported here describes detailed structural studies of endothiapepsin (the aspartic proteinase from Endothia parasitica), with and without bound inhibitors, and human pepsin 3b. Comparison of multiple crystal structures of members of the aspartic proteinase family has revealed small but significant differences in domain orientation in different crystal forms. In this paper, it is shown that these differences in domain orientation do not necessarily correlate with the presence or absence of bound inhibitors, but appear to stem at least partly from crystal contacts mediated by sulfate ions. However, since the same inherent flexibility of the structure is observed for other enzymes in this family such as human pepsin, the native structure of which is also reported here, the observed domain movements may well have implications for the mechanism of catalysis.

Berridge G, Chalk R, D'Avanzo N, Dong L, Doyle D, Kim JI, Xia X, Burgess-Brown N, Deriso A, Carpenter EP, Gileadi O. 2011. High-performance liquid chromatography separation and intact mass analysis of detergent-solubilized integral membrane proteins Analytical Biochemistry, 410 (2), pp. 272-280. | Show Abstract | Read more

We have developed a method for intact mass analysis of detergent- solubilized and purified integral membrane proteins using liquid chromatography-mass spectrometry (LC-MS) with methanol as the organic mobile phase. Membrane proteins and detergents are separated chromatographically during the isocratic stage of the gradient profile from a 150-mm C3 reversed-phase column. The mass accuracy is comparable to standard methods employed for soluble proteins; the sensitivity is 10-fold lower, requiring 0.2-5 μg of protein. The method is also compatible with our standard LC-MS method used for intact mass analysis of soluble proteins and may therefore be applied on a multiuser instrument or in a high-throughput environment. © 2010 Elsevier Inc. All rights reserved.

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Newstead S, Drew D, Cameron AD, Postis VLG, Xia X, Fowler PW, Ingram JC, Carpenter EP et al. 2011. Crystal structure of a prokaryotic homologue of the mammalian oligopeptide-proton symporters, PepT1 and PepT2 EMBO Journal, 30 (2), pp. 417-426. | Show Abstract | Read more

PepT1 and PepT2 are major facilitator superfamily (MFS) transporters that utilize a proton gradient to drive the uptake of di- and tri-peptides in the small intestine and kidney, respectively. They are the major routes by which we absorb dietary nitrogen and many orally administered drugs. Here, we present the crystal structure of PepT So, a functionally similar prokaryotic homologue of the mammalian peptide transporters from Shewanella oneidensis. This structure, refined using data up to 3.6 Å resolution, reveals a ligand-bound occluded state for the MFS and provides new insights into a general transport mechanism. We have located the peptide-binding site in a central hydrophilic cavity, which occludes a bound ligand from both sides of the membrane. Residues thought to be involved in proton coupling have also been identified near the extracellular gate of the cavity. Based on these findings and associated kinetic data, we propose that PepT So represents a sound model system for understanding mammalian peptide transport as catalysed by PepT1 and PepT2. © 2011 European Molecular Biology Organization | All Rights Reserved.

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