Catalyzes cross-linking of the peptidoglycan cell wall. Preferential cleavage: (Ac)2-L-Lys-D-Ala-|-D-Ala. Also transpeptidation of peptidyl-alanyl moieties that are N-acyl substituents of D-alanine. Cell wall biogenesis; peptidoglycan biosynthesis. Has a penicillin insensitive transglycosylase domain (formation of linear glycan strands) and a penicillin-sensitive transpeptidase domain (cross-linking of the peptide subunits). Belongs to the transpeptidase family. MrdA subfamily.