Identification of the UDP-MurNAc-Pentapeptide: l -Alanine Ligase for Synthesis of Branched Peptidoglycan Precursors in Enterococcus faecalis

Abstract
Many species of gram-positive bacteria produce branched peptidoglycan precursors resulting from the transfer of various l -amino acids or glycine from amino acyl-tRNA to the ɛ-amino group of l -lysine. The UDP-MurNAc-pentapeptide: l -alanine ligase and alanyl-tRNA synthetase genes from Enterococcus faecalis were identified, cloned, and overexpressed in Escherichia coli . The purified enzymes were necessary and sufficient for tRNA-dependent addition of l -alanine to UDP-MurNAc-pentapeptide in vitro. The ligase belonged to the Fem family of proteins, which were initially identified genetically as factors essential for methicillin resistance in Staphylococcus aureus .

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