The C terminus of penicillin-binding protein 5 is essential for localisation to the E. coli inner membrane.

Penicillin-binding protein 5 (PBP5) has been previously identified as a component of the inner membrane of Escherichia coli and we present here further evidence that PBP5 is tightly bound to the membrane. To investigate the regions of PBP5 involved in membrane binding we have constructed a series of C-terminal deletions and shown that the removal of as few as 10 amino acids results in the release of the truncated protein into the periplasm. The C terminus, therefore, appears to be important for interaction with the membrane; however, inspection of the amino acid sequence does not reveal extended runs of hydrophobicity typical of a membrane anchor. Thus we conclude that PBP5 is anchored to the inner membrane by a mechanism not previously described.