title: The cavity structure for docking the K(+)-competitive inhibitors in the gastric proton pump.
abstract: 2-Methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine-3-acetonitrile (SCH 28080) is a reversible inhibitor specific for the gastric proton pump. The inhibition pattern is competitive with K(+). Here we studied the binding sites of this inhibitor on the putative three-dimensional structure of the gastric proton pump alpha-subunit that was constructed by homology modeling based on the structure of sarcoplasmic reticulum Ca(2+) pump. Alanine and serine mutants of Tyr(801) located in the fifth transmembrane segment of the gastric proton pump alpha-subunit retained the (86)Rb transport and K(+)-dependent ATPase (K(+)-ATPase) activities. These mutants showed 60-80-times lower sensitivity to SCH 28080 than the wild type in the (86)Rb transport activity. The K(+)-ATPase activities of these mutants were not completely inhibited by SCH 28080. The sensitivity to SCH 28080 was dependent on the bulkiness of the side chain at this position. Therefore, the side chain of Tyr(801) is important for the interaction with this inhibitor. In the three-dimensional structure of the E(2) form (conformation with high affinity for K(+)) of the gastric proton pump, Tyr(801) faces a cavity surrounded by the first, fourth, fifth, sixth, and eighth transmembrane segments and fifth/sixth, seventh/eighth, and ninth/tenth loops. SCH 28080 can dock in this cavity. However, SCH 28080 cannot dock in the same location in the E(1) form (conformation with high affinity for proton) of the gastric proton pump due to the drastic rearrangement of the transmembrane helices between the E(1) and E(2) forms. These results support the idea that this cavity is the binding pocket of SCH 28080.
authors.affiliation: Life Scientific Research Center, Faculty of Pharmaceutical Sciences, Toyama Medical & Pharmaceutical University, Toyama, Japan. shinji@ms.toyama-mpc.ac.jp
authors.forename: Shinji
authors.initials: S
authors.lastname: Asano
authors.forename: Ayumi
authors.initials: A
authors.lastname: Yoshida
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yashiro
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Anna
authors.initials: A
authors.lastname: Morisato
authors.forename: Haruo
authors.initials: H
authors.lastname: Ogawa
authors.forename: Noriaki
authors.initials: N
authors.lastname: Takeguchi
authors.forename: Magotoshi
authors.initials: M
authors.lastname: Morii
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D005744:Gastric Acid / Q000378:metabolism*; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009853:Omeprazole / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011725:Pyridines / Q000737:chemistry / Q000494:pharmacology; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics*; D013270:Stomach / Q000201:enzymology*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; D011725:Pyridines; C110320:SPI 447; C035235:Sch 28080; D014443:Tyrosine; D000254:Sodium-Potassium-Exchanging ATPase; D009853:Omeprazole; D011188:Potassium