Inter-subunit interaction of gastric H+,K+-ATPase prevents reverse reaction of the transport cycle.
The gastric H(+),K(+)-ATPase is an ATP-driven proton pump responsible for generating a million-fold proton gradient across the gastric membrane. We present the structure of gastric H(+),K(+)-ATPase at 6.5 A resolution as determined by electron crystallography of two-dimensional crystals. The structure shows the catalytic alpha-subunit and the non-catalytic beta-subunit in a pseudo-E(2)P conformation. Different from Na(+),K(+)-ATPase, the N-terminal tail of the beta-subunit is in direct contact with the phosphorylation domain of the alpha-subunit. This interaction may hold the phosphorylation domain in place, thus stabilizing the enzyme conformation and preventing the reverse reaction of the transport cycle. Indeed, truncation of the beta-subunit N-terminus allowed the reverse reaction to occur. These results suggest that the beta-subunit N-terminus prevents the reverse reaction from E(2)P to E(1)P, which is likely to be relevant for the generation of a large H(+) gradient in vivo situation.
Abe
Kazuhiro
K
Department of Biophysics, Faculty of Science, Kyoto University, Kyoto, Japan.
Tani
Kazutoshi
K
Nishizawa
Tomohiro
T
Fujiyoshi
Yoshinori
Y
D020285:Cryoelectron Microscopy; D005753:Gastric Mucosa / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D017384:Sequence Deletion
D021122:Protein Subunits; D017506:H(+)-K(+)-Exchanging ATPase