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 structure of CBD reveals tandem SH3b domains that are tightly engaged with each other. CBD binds to peptidoglycan in a bidentate manner via distal β-sheet motifs with pseudo two-fold symmetry, which can explain its high affinity and host specificity. CBD primarily interacts with the glycan strand of the peptidoglycan layer instead of the peptide crosslink, implicating the tertiary structure of peptidoglycan as the recognition motif of endolysins.