Cell wall formation. Catalyzes epimerization of the terminal L-glutamate in UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-L-glutamate. ATP + H2O + UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-L-glutamate = AMP + diphosphate + H(+) + UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-D-glutamate Cell wall biogenesis; peptidoglycan biosynthesis. Belongs to the MurL family.