Different foci for the regulation of the activity of the KefB and KefC glutathione-gated K+ efflux systems

KefB and KefC are glutathione-gated K+ efflux systems in Escherichia coti, and the proteins exhibit strong similarity at the level of both primary seq uence and domain organization. The proteins are maintained closed by glutat hione and are activated by binding of adducts formed between glutathione an d electrophiles. By construction of equivalent mutations in each protein, t his study has analyzed the control over inactive state of the proteins. A U V-induced mutation in KefB, L75S, causes rapid spontaneous K+ efflux but ha s only a minor effect on K+ efflux via KefC. Similarly amino acid substitut ions that cause increased spontaneous activity in RefC have only small effe cts in RefB. Exchange of an eight amino acid region from KefC (HALESDIE) wi th the equivalent sequence from KefB (HELETAID) has identified a role for a group of acidic residues in controlling KefC activity. The mutations HELET ALD and L74S in KefC act synergistically, and the activity of the resultant protein resembles that of KefB. We conclude that, despite the high degree of sequence similarity, KefB and KefC: exhibit different sensitivities to t he same site-specific mutations.