Catalyzes the addition of L-lysine to the nucleotide precursor UDP-N-acetylmuramoyl-L-alanyl-D-glutamate (UMAG) in the biosynthesis of bacterial cell-wall peptidoglycan. Cannot use diaminopimelate as substrate. Seems to have a role in beta-lactam antibiotic resistance. ATP + L-lysine + UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-D-glutamate = ADP + H(+) + phosphate + UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gamma-D-glutamyl-L-lysine Optimum pH is 8.4-9. Cell wall biogenesis; peptidoglycan biosynthesis. Carboxylation is probably crucial for Mg(2+) binding and, consequently, for the gamma-phosphate positioning of ATP. Expression of this protein in E.coli results in 50% incorporation of L-Lys into the peptidoglycan (which normally contains meso-diaminopimelate instead), leading to abnormal morphological changes and subsequent cell lysis. Belongs to the MurCDEF family. MurE subfamily.