Catalyzes cross-linking of the peptidoglycan cell wall at the division septum (By similarity). Binds penicillin (PubMed:20580675). 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. Mainly produced during exponential phase of growth. Belongs to the transpeptidase family. FtsI subfamily.