CW_7 cell wall-binding motifs of the Cpl-7 endolysin target the peptidoglycan muropeptide

Abstract

Phage endolysins are a novel class of efficient antimicrobials (enzybiotics) by their capacity to cleave the peptidoglycan of Gram-positive bacteria in a generally species-specific manner. The Cpl-7 endolysin, a lysozyme encoded by the Cp-7 bacteriophage, is a remarkable exception among all the murein hydrolases produced by Streptococcus pneumoniae and its bacteriophages, as it degrades pneumococcal cell walls containing either choline or ethanolamine. This behavior results from the acquisition of a C-terminal module made of three identical repeats of 42 amino acid each –the CW_7 motifs – specifically involved in cell wall attachment. Preliminary investigations were indicative that CW_7 repeats recognize the peptidoglycan network as target, with the potential impact of this fact on Cpl-7 antimicrobial host range. We have proved now, using STD-NMR spectroscopy, that N-acetyl-D-glycosaminyl-(β1,4)-N-acetylmuramyl-L-alanyl-D-isoglutamine, a structural analogue of the peptidoglycan monomer, is recognized by the CW_7 repeats and the contacts provided by this ligand have been identified. This finding could also explain the identification of CW_7 motifs in proteins involved in the cell wall metabolism that are encoded by Gram-positive and Gram-negative bacteria, including several pathogens, and by bacteriophages infecting Gram-positive bacteria.