5'-aminolevulinate synthase (ALAS) catalyzes the first step in heme biosynthesis, generating 5'-aminolevulinate from glycine and succinyl-CoA. Inherited frameshift indel mutations of human erythroid-specific isozyme ALAS2, within a C-terminal (Ct) extension of its catalytic core that is only present in higher eukaryotes, lead to gain-of-function X-linked protoporphyria (XLP). Here, we report the human ALAS2 crystal structure, revealing that its Ct-extension folds onto the catalytic core, sits atop the active site, and precludes binding of substrate succinyl-CoA. The Ct-extension is therefore an autoinhibitory element that must re-orient during catalysis, as supported by molecular dynamics simulations. Our data explain how Ct deletions in XLP alleviate autoinhibition and increase enzyme activity. Crystallography-based fragment screening reveals a binding hotspot around the Ct-extension, where fragments interfere with the Ct conformational dynamics and inhibit ALAS2 activity. These fragments represent a starting point to develop ALAS2 inhibitors as substrate reduction therapy for porphyria disorders that accumulate toxic heme intermediates.
Journal article
Nature communications
04/06/2020
11
Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford, OX3 7DQ, UK.
Humans, Protoporphyria, Erythropoietic, Genetic Diseases, X-Linked, Heme, Acyl Coenzyme A, 5-Aminolevulinate Synthetase, Crystallography, X-Ray, Gene Expression Regulation, Enzymologic, Catalytic Domain, Protein Conformation, Protein Binding, Substrate Specificity, Kinetics, Catalysis, Molecular Dynamics Simulation, Protein Domains