Figure 2

Bacteriophage lysins as antimicrobials. A Modular structure of Gram-positive bacteriophage endolysins. The typical endolysin against Gram-positive bacteria has a two-domain structure, an N-terminal catalytic domain and a C-terminal cell wall binding domain. Some endolysins incorporate a 2^nd catalytic domain with a catalytic mechanism different from the first catalytic domain. Targeting different parts of the peptidoglycan, catalytic domains can include l-alanine amidase, endopeptidase, muramidase, glucosaminidase, or lytic transglycosylase activities. Cell wall binding domains may contain single or multiple binding motifs. B Modular structure of Gram-negative bacteriophage endolysins, and of engineered Artilysins. The typical endolysin against Gram-negative bacteria has only a catalytic domain. Those Gram-negative endolysins with a cell wall binding domain have it located at the N-terminus of the protein. Gram-negative endolysins do not function when applied externally due to the presence of the outer membrane of Gram-negative bacteria. Engineered endolysins, called Artilysins, penetrate the outer membrane of Gram-negative bacteria through the addition of polycationic (PC) or hydrophobic/amphipathic peptide sequences to the N-terminus or C-terminus of the endolysin. Artilysins are effective when applied externally to Gram-negative bacteria.