title: Structural basis for alternating access of a eukaryotic calcium/proton exchanger.
abstract: Eukaryotic Ca(2+) regulation involves sequestration into intracellular organelles, and expeditious Ca(2+) release into the cytosol is a hallmark of key signalling transduction pathways. Bulk removal of Ca(2+) after such signalling events is accomplished by members of the Ca(2+):cation (CaCA) superfamily. The CaCA superfamily includes the Na(+)/Ca(2+) (NCX) and Ca(2+)/H(+) (CAX) antiporters, and in mammals the NCX and related proteins constitute families SLC8 and SLC24, and are responsible for the re-establishment of Ca(2+) resting potential in muscle cells, neuronal signalling and Ca(2+) reabsorption in the kidney. The CAX family members maintain cytosolic Ca(2+) homeostasis in plants and fungi during steep rises in intracellular Ca(2+) due to environmental changes, or following signal transduction caused by events such as hyperosmotic shock, hormone response and response to mating pheromones. The cytosol-facing conformations within the CaCA superfamily are unknown, and the transport mechanism remains speculative. Here we determine a crystal structure of the Saccharomyces cerevisiae vacuolar Ca(2+)/H(+) exchanger (Vcx1) at 2.3 Å resolution in a cytosol-facing, substrate-bound conformation. Vcx1 is the first structure, to our knowledge, within the CAX family, and it describes the key cytosol-facing conformation of the CaCA superfamily, providing the structural basis for a novel alternating access mechanism by which the CaCA superfamily performs high-throughput Ca(2+) transport across membranes.
authors.affiliation: Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158, USA.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Waight
authors.forename: Bjørn Panyella
authors.initials: BP
authors.lastname: Pedersen
authors.forename: Avner
authors.initials: A
authors.lastname: Schlessinger
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Bonomi
authors.forename: Bryant H
authors.initials: BH
authors.lastname: Chau
authors.forename: Zygy
authors.initials: Z
authors.lastname: Roe-Zurz
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Risenmay
authors.forename: Andrej
authors.initials: A
authors.lastname: Sali
authors.forename: Robert M
authors.initials: RM
authors.lastname: Stroud
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003600:Cytosol / Q000378:metabolism*; D017136:Ion Transport; D017017:Methanococcus / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D017920:Antiporters; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; C099946:VCX1 protein, S cerevisiae; D002118:Calcium