A murein DD-endopeptidase with specificity for D-Ala-meso-diaminopimelic acid (mDAP) cross-links. Its role is probably to cleave D-Ala-mDAP cross-links to allow insertion of new glycans and thus cell wall expansion. Functionally redundant with MepM and MepH (By similarity). Cell wall biogenesis; cell wall polysaccharide biosynthesis. Belongs to the peptidase M23B family.