title: Dephosphorylation of the calcium pump coupled to counterion occlusion.
abstract: P-type ATPases extract energy by hydrolysis of adenosine triphosphate (ATP) in two steps, formation and breakdown of a covalent phosphoenzyme intermediate. This process drives active transport and countertransport of the cation pumps. We have determined the crystal structure of rabbit sarcoplasmic reticulum Ca2+ adenosine triphosphatase in complex with aluminum fluoride, which mimics the transition state of hydrolysis of the counterion-bound (protonated) phosphoenzyme. On the basis of structural analysis and biochemical data, we find this form to represent an occluded state of the proton counterions. Hydrolysis is catalyzed by the conserved Thr-Gly-Glu-Ser motif, and it exploits an associative nucleophilic reaction mechanism of the same type as phosphoryl transfer from ATP. On this basis, we propose a general mechanism of occluded transition states of Ca2+ transport and H+ countertransport coupled to phosphorylation and dephosphorylation, respectively.
authors.affiliation: Centre for Structural Biology, Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Olesen
authors.forename: Thomas Lykke-Møller
authors.initials: TL
authors.lastname: Sørensen
authors.forename: Rikke Christina
authors.initials: RC
authors.lastname: Nielsen
authors.forename: Jesper Vuust
authors.initials: JV
authors.lastname: Møller
authors.forename: Poul
authors.initials: P
authors.lastname: Nissen
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D017607:Aluminum Compounds / Q000737:chemistry; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000378:metabolism; D005459:Fluorides / Q000737:chemistry; D006868:Hydrolysis; D017136:Ion Transport; D008956:Models, Chemical; D008958:Models, Molecular; D010766:Phosphorylation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011522:Protons; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D019284:Thapsigargin; D013816:Thermodynamics
chemical_list: D017607:Aluminum Compounds; D011522:Protons; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride