Fig. 4.

Organization strategies of staphylococcal phage endolysins. a) Four endolysin synthesis strategies found in staphylococcal phage genomes (n = 205), 175 phages encode lysins with single genes, 20 phage lysin genes exhibit group I introns, nine phages encode lysins using two adjacent genes; one phage, 2638A, uses a single gene with an inter-lytic-domain secondary translational start site, described here [35]; b) Schematic representation of a S. aureus bacteria cell wall and peptidoglycan. The red arrow indicates the conserved glycine peptidoglycan bridge recognized by the SH3 binding domain. Black arrows indicate possible cutting sites of the catalytic domains: 1) N-acetyl-β-D-glucosaminidase, 2) N-acetyl- β -D-muramidase, 3) lytic transglycosylase, 4) N-acetylmuramoyl- L -alanine amidase, 5) L -alanyl-D-glutamate endopeptidase, 6) D -alanyl-glycyl endopeptidase, 7) L-alanoyl-D-glutamate endopeptidase. Endolysins of class 4) and 6) have been experimental validated [60]. Acronyms: CHAP, cysteine/histidine-dependent amidohydrolase/peptidase domain (PF05257/IPR007921); AMI-2, Amidase_2 domain (PF01510/IPR002502); AMI-3, Amidase_3 domain (PF01520/IPR002508); SH3–5, SH3_5 domain (PF08460/IPR013667); NAG, β-1,4-linked monomers of N-acetyl glucosamine; NAM; N-acetyl muramic acid