title: The Vibrio cholerae Mrp system: cation/proton antiport properties and enhancement of bile salt resistance in a heterologous host.
abstract: The mrp operon from Vibrio cholerae encoding a putative multisubunit Na(+)/H(+) antiporter was cloned and functionally expressed in the antiporter-deficient strain of Escherichia coli EP432. Cells of EP432 expressing Vc-Mrp exhibited resistance to Na(+) and Li(+) as well as to natural bile salts such as sodium cholate and taurocholate. When assayed in everted membrane vesicles of the E. coli EP432 host, Vc-Mrp had sufficiently high antiport activity to facilitate the first extensive analysis of Mrp system from a Gram-negative bacterium encoded by a group 2 mrp operon. Vc-Mrp was found to exchange protons for Li(+), Na(+), and K(+) ions in pH-dependent manner with maximal activity at pH 9.0-9.5. Exchange was electrogenic (more than one H(+) translocated per cation moved in opposite direction). The apparent K(m) at pH 9.0 was 1.08, 1.30, and 68.5 mM for Li(+), Na(+), and K(+), respectively. Kinetic analyses suggested that Vc-Mrp operates in a binding exchange mode with all cations and protons competing for binding to the antiporter. The robust ion antiport activity of Vc-Mrp in sub-bacterial vesicles and its effect on bile resistance of the heterologous host make Vc-Mrp an attractive experimental model for the further studies of biochemistry and physiology of Mrp systems.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Man., Canada.
authors.forename: Judith
authors.initials: J
authors.lastname: Dzioba-Winogrodzki
authors.forename: Olga
authors.initials: O
authors.lastname: Winogrodzki
authors.forename: Terry A
authors.initials: TA
authors.lastname: Krulwich
authors.forename: Markus A
authors.initials: MA
authors.lastname: Boin
authors.forename: Claudia C
authors.initials: CC
authors.lastname: Häse
authors.forename: Pavel
authors.initials: P
authors.lastname: Dibrov
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001647:Bile Acids and Salts / Q000378:metabolism*; D002412:Cations; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008094:Lithium / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D011522:Protons; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism*; D014734:Vibrio cholerae / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001647:Bile Acids and Salts; D002412:Cations; D004269:DNA, Bacterial; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D008094:Lithium; D012964:Sodium