An FTIR investigation into the lipid interactions of peptides corresponding to the C-terminal anchoring regions of Escherichia coli penicillin-binding proteins 4 and 5

The Escherichia coli low molecular mass penicillin-binding proteins (PBPs) PBP4 and PBP5 are cell wall enzymes, which bind to the periplasmic face of the inner membrane. For PBP5, this binding is considered to proceed via a C -terminal amphiphilic alpha -helix and for PBP4, a similar mechanism has be en proposed. Studies on a peptide homologue of the PBP5 C-terminal region, P5, have suggested that the strength of PBP5-membrane binding may be relate d to levels of alpha -helicity possessed by this C-terminal region. Here, w e have used FTIR spectroscopy to investigate this possibility for both PBP4 and PBP5 by conformational analysis of P5 and a PBP4 C-terminal homologue, P4, in the presence of vesicles formed from either: DMPG, DMPC DMPE or DOP C. Additionally, conductance measurements were used to investigate the abil ity of P4 to interact with DOPC planar bilayers. Our results support the pr oposal that PBP5 interacts with the membrane via a C-terminal amphiphilic a lpha -helix and also suggest that the strength of PBP4-membrane anchoring m ay also be related to levels of alpha -helicity possessed by the proteins' C-terminal region. The data also support the view that there are essential differences between the membrane anchoring mechanisms of PBP4 and PBP5.