Mrp-dependent Na(+)/H(+) antiporters of Bacillus exhibit characteristics that are unanticipated for completely secondary active transporters.
The Na(+)/H(+) antiport activity encoded by the seven-gene mrp operons of Bacillus subtilis and alkaliphilic Bacillus pseudofirmus OF4 were cloned into a low copy plasmid, were expressed in several Escherichia coli mutant strains and compared side-by-side with similarly cloned nhaA, a major secondary antiporter from E. coli. All three antiporter systems exhibited electron donor-dependent antiport in a fluorescence-based vesicle assay, with NhaA being the most active. In whole cells of the same antiporter-deficient strain from which the vesicles were made, E. coli KNabc, Mrp-mediated Na(+) exclusion was significantly more protonophore-resistant than that conferred by NhaA. The Mrp systems were also more efficacious than NhaA: in supporting anaerobic Na(+) resistance in wild type and a terminal oxidase mutant strain of E. coli (SBS2115); and in increasing non-fermentative growth of an NADH dehydrogenase-minus E. coli mutant (ANN0222). The results suggest the possibility that the Mrp systems may have both secondary and primary energization capacities.
Ito
M
M
Faculty of Life Scienes, Toyo University, Gunma, Japan. ito1107@toyonet.toyo.ac.jp
Guffanti
A A
AA
Krulwich
T A
TA
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000165:Acridine Orange / Q000494:pharmacology; D001407:Bacillus / Q000378:metabolism*; D001692:Biological Transport; D001693:Biological Transport, Active; D003001:Cloning, Molecular; D004396:Coloring Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D000165:Acridine Orange; D004396:Coloring Agents; D029968:Escherichia coli Proteins; D006859:Hydrogen; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012964:Sodium; D012965:Sodium Chloride; D017923:Sodium-Hydrogen Exchangers; C102839:NhaA protein, E coli