title: Differences in the phenotypic effects of mutations in homologous MrpA and MrpD subunits of the multi-subunit Mrp-type Na+/H+antiporter.
abstract: Mrp antiporters are the sole antiporters in the Cation/Proton Antiporter 3 family of transporter databases because of their unusual structural complexity, 6-7 hydrophobic proteins that function as a hetero-oligomeric complex. The two largest and homologous subunits, MrpA and MrpD, are essential for antiport activity and have direct roles in ion transport. They also show striking homology with proton-conducting, membrane-embedded Nuo subunits of respiratory chain complex I of bacteria, e.g., Escherichia coli. MrpA has the closest homology to the complex I NuoL subunit and MrpD has the closest homology to the complex I NuoM and N subunits. Here, introduction of mutations in MrpD, in residues that are also present in MrpA, led to defects in antiport function and/or complex formation. No significant phenotypes were detected in strains with mutations in corresponding residues of MrpA, but site-directed changes in the C-terminal region of MrpA had profound effects, showing that the MrpA C-terminal region has indispensable roles in antiport function. The results are consistent with a divergence in adaptations that support the roles of MrpA and MrpD in secondary antiport, as compared to later adaptations supporting homologs in primary proton pumping by the respiratory chain complex I.
authors.affiliation: Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA.|, 573-13 Kamitanui, Tarnaki-cho, Watarai-gun, Mie, 519-0417, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Morino
authors.affiliation: Faculty of Life Sciences, Graduate School of Life Sciences, Toyo University, Oura-gun, Gunma, 374-0193, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Ogoda
authors.affiliation: Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA.
authors.forename: Terry Ann
authors.initials: TA
authors.lastname: Krulwich
authors.affiliation: Faculty of Life Sciences, Graduate School of Life Sciences, Toyo University, Oura-gun, Gunma, 374-0193, Japan. masahiro.ito@toyo.jp.|Bio-Nano Electronics Research Center, Toyo University, Kawagoe, Saitama, 350-0815, Japan. masahiro.ito@toyo.jp.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ito
mesh_terms: D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D000072417:Protein Domains; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D021122:Protein Subunits; D017923:Sodium-Hydrogen Exchangers
keywords: Alkaliphiles; Cation/proton antiporter; Complex I; Mrp