GerN, an Endospore Germination Protein of Bacillus cereus, Is an Na super(+)/H super(+)-K super(+) Antiporter

• Published in: Journal of bacteriology Vol. 183; no. 20; pp. 5896 - 5903
• Main Authors: Southworth, T W, Guffanti, A A, Moir, A, Krulwich, T A
• Format: Journal Article
• Language: English
• Published: 01.10.2001
• Subjects: antiporters; Bacillus cereus; GerN protein
• ISSN: 0021-9193
• DOI: 10.1128/JB.183.20.5896-5903.2001

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 super(+)-sensitive phenotype of an Escherichia coli mutant that is deficient in Na super(+)/H super(+) antiport activity (strain KNabc). GerN also reduced the concentration of K super(+) required to support growth of an E. coli mutant deficient in K super(+) uptake (strain TK2420). In a fluorescence-based assay of everted E. coli KNabc membrane vesicles, GerN exhibited robust Na super(+)/H super(+) antiport activity, with a K sub(m) for Na super(+) estimated at 1.5 mM at pH 8.0 and 25 mM at pH 7.0. Li super(+), but not K super(+), served as a substrate. GerN-mediated Na super(+)/H super(+) antiport was further demonstrated in everted vesicles as energy-dependent accumulation of super(22)Na super(+). GerN also used K super(+) as a coupling ion without completely replacing H super(+), as indicated by partial inhibition by K super(+) of H super(+) uptake into right-side-out vesicles loaded with Na super(+). K super(+) translocation as part of the antiport was supported by the stimulatory effect of intravesicular K super(+) on super(22)Na super(+) uptake by everted vesicles and the dependence of GerN-mediated super( 86)Rb super(+) efflux on the presence of Na super(+) in trans. The inhibitory patterns of protonophore and thiocyanate were most consistent with an electrogenic Na super(+)/H super(+)-K super(+) antiport. GerN-mediated Na super(+)/H super(+)-K super(+) antiport was much more rapid than GerN-mediated Na super(+)/H super(+ )antiport.