1.A.73 The Colicin Lysis Protein (CLP) Family
The lipopeptides of the CLP family are found in closely related γ-proteobacteria (E. coli, Klebsiella, Shigella, Citrobacter) and are usually plasmid-encoded with the colicin they secrete. They can be specific for various group A colicins which are secreted, in contrast to group B colicins which are not. Secretion involves CLP family lipopeptides and allows secretion across both membranes of the envelope of the producing bacterium. The chains are released in the medium late after synthesis. They function in the export of various colicins (E1-9, K, A10, D-157, N, S4 and U). These peptide precursors of 45-100 aas are acylated and processed in the inner membrane before being exported to the outer membrane. They exhibit one N-terminal putative signal sequence followed by a conserved cysteine residue and a C-terminal hydrophilic region (Cavard, 2002)
The lysis protein (47 aas; 1 TMS) of the colicinogenic operon is essential for colicin release; it functions to activate the outer membrane phospholipase A (OMPLA) for export of colicin across the outer cell envelope. Cells with the wild-type mature LysE7 protein exhibit higher efficiency of colicicn E7 translocation across the inner membrane into the periplasm than those with the mutant LysE7 protein. The degree of inner membrane permeability induced by the mature LysE7 protein is greater than by the unmodified LysE7 precursor. The efficiency of colicin movement into the periplasm correlates with the increase in inner membrane permeability induced by LysE7 (Chen et al., 2011). Thus, the mature LysE7 protein has two critical roles: firstly, mediating the translocation of colicin E7 across the inner membrane into the periplasm, and secondly activating the OMPLA to allow colicin release (Chen et al., 2011).