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Sodium/calcium (Na(+)/Ca(2+)) exchangers (NCX) are membrane transporters that play an essential role in maintaining the homeostasis of cytosolic Ca(2+) for cell signaling. We demonstrated the Na(+)/Ca(2+)-exchange function of an NCX from Methanococcus jannaschii (NCX_Mj) and report its 1.9 angstrom crystal structure in an outward-facing conformation. Containing 10 transmembrane helices, the two halves of NCX_Mj share a similar structure with opposite orientation. Four ion-binding sites cluster at the center of the protein: one specific for Ca(2+) and three that likely bind Na(+). Two passageways allow for Na(+) and Ca(2+) access to the central ion-binding sites from the extracellular side. Based on the symmetry of NCX_Mj and its ability to catalyze bidirectional ion-exchange reactions, we propose a structure model for the inward-facing NCX_Mj.

Original publication




Journal article


Science (New York, N.Y.)

Publication Date





686 - 690


Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.


Methanococcales, Sodium, Calcium, Archaeal Proteins, Sodium-Calcium Exchanger, Ligands, Crystallization, Crystallography, X-Ray, Binding Sites, Ion Transport, Amino Acid Sequence, Protein Conformation, Protein Structure, Secondary, Models, Molecular, Molecular Sequence Data