Direct CIII-HflB interaction is responsible for the inhibition of the HflB (FtsH)-mediated proteolysis of Escherichia coli sigma(32) by lambda CIII

Abstract

The CIII protein of bacteriophage lambda exhibits antiproteolytic activity against the ubiquitous metalloprotease HflB (FtsH) of Escherichia coli, thereby stabilizing the lambda CII protein and promoting lysogenic development of the phage. CIII also protects E. coli sigma(32), another substrate of HflB. We have recently shown that the protection of CII from HflB by CIII involves direct CIII-HflB binding, without any interaction between CII and CIII [Halder S, Datta AB & Parrack P (2007) J Bacteriol 189, 8130-8138]. Such a mode of action for lambda CIII would be independent of the HflB substrate. In this study, we tested the ability of CIII to protect sigma(32) from HflB digestion. The inhibition of HflB-mediated proteolysis of sigma(32) by CIII is very similar to that of lambda CII, characterized by an enhanced protection by the core CIII peptide CIIIC (amino acids 14-41 of lambda CIII) and a lack of interaction between sigma(32) and CIII.