Biosynthesis of peptidoglycan in Staphylococcus aureus: incorporation of the N(ε) Ala Lys moiety into the peptide subunit of nascent peptidoglycan

Abstract

UDP MurNAc Ala DGlu Lys (Nε Ala) DAla DAla was isolated form extracts of S. aureus Copenhagen. This nucleotide accumulated in media deficient in glycine. To establish its role in peptidoglycan biosynthesis, the nucleotide hexapeptide was compared with UDP MurNAc Ala DGlu Lys DAla DAla in the reaction catalyzed by phospho MurNAc pentapeptide translocase and in the membrane catalyzed nascent peptidoglycan synthesizing system. In the exchange reaction catalyzed by the translocase, the R(max) and R(max) K(m) are 1.79 μM/min and 4.47 x 10-2/min, respectively, for UDP MurNAc pentapeptide and 1.81 μM/min and 4.46 x 10-2/min, respectively, for UDP MurNAc hexapeptide. In the synthesis of nascent peptidoglycan, the V(max) is 1.8 μM/min x 10-2 for both the nucleotide hexapeptide and pentapeptide. The V(max)/K(m) is 5.6 x 10-4 and 4.3 x 10-4/min for the nucleotide pentapeptide and hexapeptide, respectively. Schleifer, Hammes, and Kandler observed that growth of S. aureus Copenhagen on a glycine poor medium results in a peptidoglycan structure in which 20% of the lysine residues are substituted at the ε amino group by L alanine residues that do not participate in interpeptide bridge formation. The in vitro studies demonstrate that UDP MurNAc Ala DGlu Lys(Nε Ala) DAla DAla is a possible precursor of the Nε Ala Lys moiety.