Reutilizes the intact tripeptide L-alanyl-gamma-D-glutamyl-meso-diaminopimelate by linking it to UDP-N-acetylmuramate. 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 Cell wall biogenesis; peptidoglycan recycling. Belongs to the MurCDEF family. Mpl subfamily.