Muralytic enzyme exposed to host peptidoglycan layer after membrane fusion during viral entry. Functions as an exolysin that cleaves the peptide bridge formed by meso-diaminopimelic acid and D-alanine. Also lyses the host cell late in infection to release the virions. Optimum pH is 8.5. Inactivated at temperatures above 20 degrees Celsius. Monomer. Located between the capsid and the envelope. Belongs to the peptidase U40 family. It is uncertain whether Met-1 or Val-9 is the initiator.