Identification of the UDP-MurNAc-pentapeptide : L-alanine ligase for synthesis of branched peptidoglycan precursors in Enterococcus faecalis

Many species of gram-positive bacteria produce branched peptidoglycan precu rsors resulting from the transfer of various L-amino acids or glycine from amino acyl-tRNA to the epsilon -amino group of L-lysine. The UDP-MurNAc-pen tapeptide:L-alanine ligase and alanyl-tRNA synthetase genes from Enterococc us faecalis were identified, cloned, and overexpressed in Escherichia coli. The purified enzymes were necessary and sufficient for tRNA-dependent addi tion of L-alanine to UDP-MurNAc-pentapeptide in vitro. The ligase belonged to the Fern family of proteins, which were initially identified genetically as factors essential for methicillin resistance in Staphylococcus aureus.