title: Intermolecular cross-linking of monomers in Helicobacter pylori Na+/H+ antiporter NhaA at the dimer interface inhibits antiporter activity.
abstract: We have previously shown that HPNhaA (Helicobacter pylori Na+/H+ antiporter) forms an oligomer in a native membrane of Escherichia coli, and conformational changes of oligomer occur between monomers of the oligomer during ion transport. In the present study, we use Blue-native PAGE to show that HPNhaA forms a dimer. Cysteine-scanning mutagenesis of residues 55-61 in a putative beta-sheet region of loop1 and subsequent functional analyses revealed that the Q58C mutation resulted in an intermolecular disulfide bond. G56C, I59C and G60C were found to be cross-linked by bifunctional cross-linkers. Furthermore, the Q58E mutant did not form a dimer, possibly due to electrostatic repulsion between monomers. These results imply that Gln-58 and the flanking sequence in the putative beta-sheet of the monomer are located close to the identical residues in the dimer. The Q58C mutant of NhaA was almost inactive under non-reducing conditions, and activity was restored under reducing conditions. This result showed that cross-linking at the dimer interface reduces transporter activity by interfering with the flexible association between the monomers. A mutant HPNhaA protein with three amino acid substitutions at residues 57-59 did not form a dimer, and yet was active, indicating that the monomer is functional.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan. kanazawa@bio.sci.osaka-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Karasawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Mitsui
authors.forename: Masafumi
authors.initials: M
authors.lastname: Matsushita
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kanazawa
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D016480:Helicobacter pylori / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D017923:Sodium-Hydrogen Exchangers