Reutilizes the intact tripeptide L-alanyl-gamma-D-glutamyl-meso-diaminopimelate by linking it to UDP-N-acetylmuramate. The enzyme can also use the tetrapeptide L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioyl-D-alanine or the pentapeptide L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptandioyl-D-alanyl-D-alanine in vivo and in vitro. ATP + L-alanyl-gamma-D-glutamyl-meso-diaminoheptanedioate + UDP-N-acetyl-alpha-D-muramate = ADP + H(+) + phosphate + UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate kcat is 290 min(-1). Optimum pH is 8.4. Cell wall biogenesis; peptidoglycan recycling. Enzyme ligase activity totally absent. No effect on growth. Belongs to the MurCDEF family. Mpl subfamily.