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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

DOI

10.1126/science.1215759

Type

Journal article

Journal

Science

Publication Date

10/02/2012

Volume

335

Pages

686 - 690

Keywords

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