Catalysis of the reaction: ATP + UDP-N-acetyl-alpha-D-muramate + L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate = ADP + phosphate + UDP-N-acetylmuramoyl-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate.
murein peptide ligase