title: GerN, an endospore germination protein of Bacillus cereus, is an Na(+)/H(+)-K(+) antiporter.
abstract: GerN, a Bacillus cereus spore germination protein, exhibits homology to a widely distributed group of putative cation transporters or channel proteins. GerN complemented the Na(+)-sensitive phenotype of an Escherichia coli mutant that is deficient in Na(+)/H(+) antiport activity (strain KNabc). GerN also reduced the concentration of K(+) required to support growth of an E. coli mutant deficient in K(+) uptake (strain TK2420). In a fluorescence-based assay of everted E. coli KNabc membrane vesicles, GerN exhibited robust Na(+)/H(+) antiport activity, with a K(m) for Na(+) estimated at 1.5 mM at pH 8.0 and 25 mM at pH 7.0. Li(+), but not K(+), served as a substrate. GerN-mediated Na(+)/H(+) antiport was further demonstrated in everted vesicles as energy-dependent accumulation of (22)Na(+). GerN also used K(+) as a coupling ion without completely replacing H(+), as indicated by partial inhibition by K(+) of H(+) uptake into right-side-out vesicles loaded with Na(+). K(+) translocation as part of the antiport was supported by the stimulatory effect of intravesicular K(+) on (22)Na(+) uptake by everted vesicles and the dependence of GerN-mediated (86)Rb(+) efflux on the presence of Na(+) in trans. The inhibitory patterns of protonophore and thiocyanate were most consistent with an electrogenic Na(+)/H(+)-K(+) antiport. GerN-mediated Na(+)/H(+)-K(+) antiport was much more rapid than GerN-mediated Na(+)/H(+) antiport.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: T W
authors.initials: TW
authors.lastname: Southworth
authors.forename: A A
authors.initials: AA
authors.lastname: Guffanti
authors.forename: A
authors.initials: A
authors.lastname: Moir
authors.forename: T A
authors.initials: TA
authors.lastname: Krulwich
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D001409:Bacillus cereus / Q000235:genetics / Q000254:growth & development*; D001426:Bacterial Proteins; D001693:Biological Transport, Active; D002414:Cations, Monovalent / Q000378:metabolism; D016764:Cell Polarity; D004926:Escherichia coli / Q000235:genetics; D005816:Genetic Complementation Test; D008566:Membranes / Q000378:metabolism; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D012975:Sodium Isotopes; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013171:Spores, Bacterial / Q000254:growth & development
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D002414:Cations, Monovalent; C419208:GerN protein, Bacillus cereus; D012975:Sodium Isotopes; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D012413:Rubidium; D011188:Potassium