ALPHA-HELICAL CONFORMATION IN THE C-TERMINAL ANCHORING DOMAINS OF ESCHERICHIA-COLI PENICILLIN-BINDING PROTEIN-4, PROTEIN-5 AND PROTEIN-6

The E, coli low molecular mass penicillin-binding proteins (PBP's) are penicillin sensitive, enzymes involved in the terminal stages of pept idoglycan biosynthesesis. These PBP's are believed to anchor to the pe riplasmic face of the inner membrane via C-terminal amphiphilic alpha- helices but to date the only support for this hypothesis has been obta ined from theoretical analysis. In this paper, the conformational beha viour of synthetic peptides corresponding to these C-terminal anchorin g domains was studied as a function of solvent, pH, sodium dodecyl sul phate micelles and phospholipid (DOPC, DOPG) vesicles using circular d ichroism (CD) spectroscopy. The CD data showed that in 2,2,2-trifluoro ethanol or sodium dodecylsulphate, all three peptides have the capacit y to form an alpha-helical conformation but in aqueous solution or in the presence of phospholipid vesicles only those peptides correspondin g to the PBP5 and PBP6 C-termini were observed to do so. A pH dependen t loss of alpha-helical conformation in the peptide corresponding to t he PBP5 C-terminus was found to correlate with the susceptibility of P BP5 to membrane extraction. This correlation would agree with the hypo thesis that an alpha-helical conformation is required for membrane int eraction of the PBP5 C-terminal region. (C) 1997 Elsevier Science B.V.