Fig. 3

The function of endolysin catalytic domains encoded by phages infecting G⁺ bacteria. A Schematic representation of the G⁺ bacterial cell wall. B Diagram of the peptidoglycan bonds cleaved by different endolysins. MurNAc and GlcNAc are repeating units of the glycan strands that are linked to a stem peptide through an amide bond to the MurNAc. Stem peptides are then cross-linked through a pentaglycine (in the case of S. aureus) to adjacent stem peptides forming a tight stable net around the bacterium. Based on the cleaved chemical bonds within the peptidoglycan layer, endolysins have several enzyme activities, including muramidase (N-acetylmuramidase), glucosaminidase (N-acetyl-β-D-glucosaminidases), amidase (N-acetylmuramoyl-L-alanine amidase), and endopeptidase (L-alanoyl-D-glutamate endopeptidase or interpeptide bridge-specific endopeptidases). MurNAc N-acetyl muramic acid, GlcNAc N-acetyl glucosamine, L-Ala L-alanine, D-iso-Glu D-iso-glutamic acid, L-Lys L-lysine, D-Ala D-alanine. *β-1,4 glycosidic bond between MurNAc and GlcNAc. ▼β-1,4 glycosidic bond between GlcNAc and MurNAc. #amide bond between MurNAc and L-Ala. ★peptide bond between two amino acids