Membrane interaction of Escherichia coli penicillin binding protein 5 is modulated by the ectomembranous domain

E. coli penicillin binding protein (PBP) 5 is anchored to the periplasmic face of the inner membrane by a C-terminal domain which is predicted to form an amphiphilic alpha-helix. Here we show that the presence of a substrate analogue, benzyl penicillin, causes the protein to be converted from a membrane bound urea inaccessible form to a urea extractable form. If the anchor region is fused to the periplasmic protein, beta-lactamase, the fusion protein becomes membrane bound but is unable to exhibit the changes in urea extractability which are observed with PBP5. We therefore conclude that although the C-terminus of PBP5 is sufficient to anchor the protein to the membrane surface the ectomembranous domain can affect the state of the anchor and in vivo changes in the state of anchoring may be related to enzyme activity.