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Roles of transmembrane segment M1 of Na+,K+-ATPase and Ca2+-ATPase, the gatekeeper and the pivot
Authors:Anja Pernille Einholm  Jens Peter Andersen  Bente Vilsen
Affiliation:(1) Institute of Physiology and Biophysics, University of Aarhus, Aarhus, Denmark;(2) Department of Physiology, Institute of Physiology and Biophysics, University of Aarhus, 1160 Ole Worms Allé, Aarhus C, 8000, Denmark
Abstract:In this review we summarize mutagenesis work on the structure–function relationship of transmembrane segment M1 in the Na+,K+-ATPase and the sarco(endo)plasmic reticulum Ca2+-ATPase. The original hypothesis that charged residues in the N-terminal part of M1 interact with the transported cations can be rejected. On the other hand hydrophobic residues in the middle part of M1 turned out to play crucial roles in Ca2+ interaction/occlusion in Ca2+-ATPase and K+ interaction/occlusion in Na+,K+-ATPase. Leu65 of the Ca2+-ATPase and Leu99 of the Na+,K+-ATPase, located at homologous positions in M1, function as gate-locking residues that restrict the mobility of the side chain of the cation binding/gating residue of transmembrane segment M4, Glu309/Glu329. A pivot formed between a pair of a glycine and a bulky residue in M1 and M3 seems critical to the opening of the extracytoplasmic gate in both the Ca2+-ATPase and the Na+,K+-ATPase. All numbering of Na+,K+-ATPase amino acid residues in this article refers to the sequence of the rat α1-isoform.
Keywords:Na+,K+-ATPase  Ca2+-ATPase  Transmembrane segment M1  Ion occlusion  Leucine  P-type ATPase  Gating
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