Interaction of the transmembrane domain of lysis protein E from bacteriophage phi X174 with bacterial translocase MraY and peptidyi-prolyl isomerase SlyD

The molecular target for the bacteriolytic E protein from bacteriophage phi Chi 174, responsible for host cell lysis, is known to be the enzyme phospho-MurNAc-pentapeptide translocase (MraY), an integral membrane protein involved in bacterial cell wall peptidoglycan biosynthesis, with an essential role being played by peptidyl-prolyl isomerase SlyD. A synthetic 37 aa peptide E-pep, containing the N-terminal transmembrane alpha-helix of E, was found to be bacteriolytic against Bacillus licheniformis, and inhibited membrane-bound MraY. The solution conformation of E-pep was found by circular dichroism (CD) spectroscopy to be 100% alpha-helical. No change in the CD spectrum was observed upon addition of purified Escherichia coli SlyD, implying that SlyD does not catalyse prolyl isomerization upon E. However, E-pep was found to be a potent inhibitor of SlyD-catalysed peptidylprolyl isomerization (IC50 0.15 mu M), implying a strong interaction between E and SlyD. E-pep was found to inhibit E coli MraY activity when assayed in membranes (IC50 0.8 mu M); however, no inhibition of solubilized MraY was observed, unlike nucleoside natural product inhibitor tunicamycin. These results imply that the interaction of E with MraY is not at the MraY active site, and suggest that a protein-protein interaction is formed between E and MraY at a site within the transmembrane region