Structural Basis for Cell-Wall Recognition by Bacteriophage PBC5 Endolysin

Phage endolysins are hydrolytic enzymes that cleave the bacterial cell wall during the lytic cycle. We isolated the bacteriophage PBC5 against Bacillus cereus, a major foodborne pathogen, and describe the molecular interaction between endolysin LysPBC5 and the host peptidoglycan structure. LysPBC5 has an N-terminal glycoside hydrolase 25 domain, and a C-terminal cell-wall binding domain (CBD) that is critical for specific cell-wall recognition and lysis. The crystal and solution structures of CBDs reveal tandem SH3b domains that are tightly engaged with each other. The CBD binds to the peptidoglycan in a bidentate manner via distal beta sheet motifs with pseudo 2-fold symmetry, which can explain its high affinity and host specificity. The CBD primarily interacts with the glycan strand of the peptidoglycan layer instead of the peptide cross-link, implicating the tertiary structure of peptidoglycan as the recognition motif of endolysins.