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Mrp‐dependent Na + /H + antiporters of Bacillus exhibit characteristics that are unanticipated for completely secondary active transporters
Author(s) -
Ito Masahiro,
Guffanti Arthur A.,
Krulwich Terry A.
Publication year - 2001
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(01)02417-6
Subject(s) - antiporter , protonophore , escherichia coli , antiporters , bacillus subtilis , mutant , biochemistry , chemistry , vesicle , electrochemical gradient , biology , bacteria , membrane , gene , genetics
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.