Penicillin-binding protein 5 expressed by E. coli (Swiss:P04287) functions as a D-alanyl-D-alanine carboxypeptidase. It is composed of two domains that are oriented at approximately right angles to each other. The N-terminal domain (Pfam:PF00768) is the catalytic domain. The C-terminal domain featured in this family is organised into a sandwich of two anti-parallel beta-sheets, and has a relatively hydrophobic surface as compared to the N-terminal domain. Its precise function is unknown; it may mediate interactions with other cell wall-synthesising enzymes, thus allowing the protein to be recruited to areas of active cell wall synthesis. It may also function as a linker domain that positions the active site in the catalytic domain closer to the peptidoglycan layer, to allow it to interact with cell wall peptides [1].

1: Crystal structure of a deacylation-defective mutant of penicillin-binding protein 5 at 2.3-A resolution. Davies C, White SW, Nicholas RA; J Biol Chem 2001;276:616-623. PMID:10967102