Escherichia coli HflK and HflC can individually inhibit the HflB (FtsH)-mediated proteolysis of λCII in vitro

lambda CII is the key protein that influences the lysis/lysogeny decision of by activating several phage promoters The effect of CII is modulated by a number of phage and host proteins including Escherichia colt HflK and HflC These membrane proteins copurify as a tightly bound complex 'HflKC' that inhibits the HfIB (FtsH)mediated proteolysis of CII both in vitro and in vivo Individual purification of HflK and HflC has not been possible so far, since each requires the presence of the other for proper folding. We report the first purification of HflK and HfIC separately as active and functional proteins and show that each can interact with HflB on its own and each inhibits the proteolysis of CII They also inhibit the proteolysis of E colt sigma(32) by HflB We show that at low concentrations each protein is dimeric, based on which we propose a scheme for the mutual interactions of HflB, HflC and HfIC in a supramolecular HflBKC protease complex (C) 2010 Elsevier Inc. All rights reserved