A molecular analysis of the potassium efflux system KefC
KefB and KefC are glutathione-gated potassium channels that play a protective role during the detoxification of electrophiles in Gram negative bacteria. The KefC channel from Klebsiella aerogenes has been characterised and the gene cloned and sequenced. The KefC channel from K. aerogenes is analogous to KefC from Escherichia coli. The electrophile compounds NEM and CDNB are strong activators of potassium loss via the channel, whereas, methylglyoxal is a weak activator of potassium loss. At the amino acid level the putative protein shows a high degree of similarity with KefC from E. coli. While sequencing the kefC gene from K. aerogenes a difference in the genome organisation of K. aerogenes and E. coli was observed, highlighting the presence of an unassigned ORF, yabF, that overlaps the kefC by 8 bp. Clones of the K. aerogenes kefC gene that lack the first 129 bp of yabF exhibit reduced KefC activity. Analysis of the sequence surrounding the kefB gene from E. coli revealed an ORF, yhaH, that encodes a homologue of the putative YabF protein. The amino acid distribution of YabF and YhaH predict soluble proteins with significant similarity to the NAD(P)H dehydrogenase quinone oxidoreductase, DHQV. To investigate the function of YabF, a strain lacking the yabF-kefC region in E. coli was constructed. The strain was transduced into a kefB background and when transformed with a plasmid expressing only KefC channel activity was greatly reduced. The data suggest that the YabF protein is required in trans for the activity of KefC and preliminary evidence from in vitro-galactosidase fusion studies suggest that yabF and kefC genes may form an operon.