Investigations into the mechanisms used by the C-terminal anchors of Escherichia coli penicillin-binding proteins 4, 5, 6 and 6b for membrane interaction

Authors


  • Enzymes: Escherichia coli PBP4 (EC 3.4.16.4; EC 3.4.99-); E. coli PBP5 (EC 3.4.16.4); E. coli PBP6 (EC 3.4.16.4); E. coli PBP6b (EC 3.4.16.4).

D. Phoenix, Department of Forensic and Investigative Science, University of Central Lancashire, Preston, PR1 2HE, UK. Fax: + 44 1772 894964, Tel.: + 44 1772 893481, E-mail: daphoenix@uclan.ac.uk

Abstract

Escherichia coli low molecular mass penicillin-binding proteins (PBPs) include PBP4, PBP5, PBP6 and PBP6b. Evidence suggests that these proteins interact with the inner membrane via C-terminal amphiphilic α-helices. Nonetheless, the membrane interactive mechanisms utilized by the C-terminal anchors of PBP4 and PBP6b show differences to those utilized by PBP5 and PBP6. Here, hydrophobic moment-based analyses have predicted that, in contrast to the PBP4 and PBP6b C-termini, those of PBP5 and PBP6 are candidates to form oblique orientated α-helices. Consistent with these predictions, Fourier transform infrared spectroscopy (FTIR) has shown that peptide homologs of the PBP4 and PBP5 C-terminal regions, P4 and P5, respectively, both possessed the ability to adopt α-helical structure in the presence of lipid. However, whereas P4 appeared to show a preference for interaction with the surface regions of dimyristoylglycerophosphoethanolamine and dimyristoylglycerophosphoglycerol membranes, P5 appeared to show deep penetration of both these latter membranes and dimyristoylglycerophosphocholine membranes. Based on these results, we have suggested that in contrast to the membrane anchoring of the PBP4 and PBP6b C-terminal α-helices, the PBP5 and PBP6 C-terminal α-helices may possess hydrophobicity gradients and penetrate membranes in an oblique orientation.

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