| Description | The CPA2 family is a moderately large family (over 100 sequenced members) from bacteria, archaea and eukaryotes. Among the functionally well-characterised members of the family are (1) the KefB/KefC K+ efflux proteins of Escherichia coli which may be capable of catalysing both K+/H+ antiport and K+ uniport, depending on conditions [ , ], (2) the Na+/H+ antiporter of Enterococcus hirae [] and (3) the K+/H+ antiporter of Saccharomyces cerevisiae. It has been proposed that under normal physiological conditions, these proteins may function by essentially the same mechanism [].KefC and KefB of E. coli are responsible for glutathione-gated K+ efflux [ , ]. Each of these proteins consists of a transmembrane hydrophobic N-terminal domain, and a less well-conserved C-terminal hydrophilic domain. Each protein interacts with a second protein encoded by genes that overlap the gene encoding the primary transporter. The KefB ancillary protein is YheR. The ancillary proteins stimulate transport activity about 10-fold []. They are important for cell survival during exposure to toxic metabolites, possibly because they can release K+, allowing H+ uptake. Activation of the KefB or KefC K+ efflux system only occurs in the presence of glutathione and a reactive electrophile such as methylglyoxal or N-ethylmaleimide. Formation of the methylglyoxal-glutathione conjugate, S-lactoylglutathione, is catalysed by glyoxalase I, and S-lactoylglutathione activates KefB and KefC [ ]. H+ uptake (acidification of the cytoplasm) accompanying or following K+ efflux may serve as a further protective mechanism against electrophile toxicity [, ]. Inhibition of transport by glutathione is enhanced by NADH []. | Name | Glutathione-regulated potassium-efflux system protein KefB |
| Short Name | K_H_efflux_KefB | Type | Family |
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