This is the C-terminal domain of bacteriophage PSA endolysin. The C-terminal domain is the cell wall-binding domain (CBD) which is composed of two structurally homologous subdomains. CBD comprises two copies of a beta-barrel-like folds, which are held together by means of swapped beta-strands. The observed structure of the CBD sub-domains from Listeriaphage endolysin (N-acetyl-muramoyl-l-alanine amidase), could be the result of either a gene duplication during evolution of the CBD or the pick-up of another functionally equivalent coding sequence, followed by swapping of the respective ancestral leading beta-strands [1].

1: The crystal structure of the bacteriophage PSA endolysin reveals a unique fold responsible for specific recognition of Listeria cell walls. Korndorfer IP, Danzer J, Schmelcher M, Zimmer M, Skerra A, Loessner MJ; J Mol Biol. 2006;364:678-689. PMID:17010991