A single K+-binding site in the crystal structure of the gastric proton pump
Kenta Yamamoto,
Vikas Dubey,
Katsumasa Irie,
Hanayo Nakanishi,
Himanshu Khandelia,
Yoshinori Fujiyoshi,
Kazuhiro Abe
Affiliations
Kenta Yamamoto
Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan; Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Japan
Vikas Dubey
Department of Physics, Chemistry and Pharmacy, PHYLIFE, University of Southern Denmark, Odense, Denmark
Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan; Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Japan
Hanayo Nakanishi
Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan; Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Japan
Himanshu Khandelia
Department of Physics, Chemistry and Pharmacy, PHYLIFE, University of Southern Denmark, Odense, Denmark
Yoshinori Fujiyoshi
Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan; CeSPIA Inc, Tokyo, Japan
Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan; Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Japan
The gastric proton pump (H+,K+-ATPase), a P-type ATPase responsible for gastric acidification, mediates electro-neutral exchange of H+ and K+ coupled with ATP hydrolysis, but with an as yet undetermined transport stoichiometry. Here we show crystal structures at a resolution of 2.5 Å of the pump in the E2-P transition state, in which the counter-transporting cation is occluded. We found a single K+ bound to the cation-binding site of the H+,K+-ATPase, indicating an exchange of 1H+/1K+ per hydrolysis of one ATP molecule. This fulfills the energy requirement for the generation of a six pH unit gradient across the membrane. The structural basis of K+ recognition is resolved and supported by molecular dynamics simulations, establishing how the H+,K+-ATPase overcomes the energetic challenge to generate an H+ gradient of more than a million-fold—one of the highest cation gradients known in mammalian tissue—across the membrane.
