Multiple Enzymatic Activities of the Murein Hydrolase from Staphylococcal Phage Phi11. Identification of a D-alanyl-glycine Endopeptidase Activity

Bacteriophage muralytic enzymes degrade the cell wall envelope of staphylococci to release phage particles from the bacterial cytoplasm. Murein hydrolases of staphylococcal phages phi11, 80alpha, 187, Twort, and phiPVL harbor a central domain that displays sequence homology to known N-acetylmuramyl-L-alanyl amidases; however, their precise cleavage sites on the staphylococcal peptidoglycan have thus far not been determined. Here we examined the properties of the phi11 enzyme to hydrolyze either the staphylococcal cell wall or purified cell wall anchor structures attached to surface protein. Our results show that the phi11 enzyme has D-alanyl-glycyl endopeptidase as well as N-acetylmuramyl-L-alanyl amidase activity. Analysis of a deletion mutant lacking the amidase-homologous sequence, phi11(Delta181-381), revealed that the D-alanyl-glycyl endopeptidase activity is contained within the N-terminal 180 amino acid residues of the polypeptide chain. Sequences similar to this N-terminal domain are found in the murein hydrolases of staphylococcal phages but not in those of phages that infect other Gram-positive bacteria such as Listeria or Bacillus.