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. Partially suppresses an mepS disruption mutant. Cell wall biogenesis; cell wall polysaccharide biosynthesis. A triple mepS-mepH-mepM mutant is inviable, whereas a double mepS-mepM will grow on a nutrient-poor medium but not on a rich medium, suggesting the 3 endopeptidases are functionally redundant in vivo. Depletion experiments of the double or triple mutants lead to cell lysis, as well as significantly decreased incorporation of mDAP into peptidogylcan sacculi and increased amounts of the enzyme's substrate (Tetra-Tetra-anhydro muropeptide). Belongs to the peptidase C40 family.