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. 2007 Oct 11;35(20):6870–6883. doi: 10.1093/nar/gkm778

Figure 1.

Figure 1.

Main steps of peptidoglycan synthesis in W. viridescens. The subunit consists of β-1-4-linked N-acetyl glucosamine (GlcNAc) and N-acetyl muramic acid (MurNAc) substituted by a depsipeptide which is linked to the d-lactoyl group of MurNAc by an amide bond. The assembly of the subunit starts in the cytoplasm by the synthesis of UDP-MurNAc, the first precursor dedicated to peptidoglycan synthesis (37). In the following steps, the Mur ligases sequentially add l-Ala, d-Glu, l-Lys, attached to the γ carboxyl of d-Glu (d-iGlu) and the depsipeptide d-Ala-d-Lac to form the stem pentadepsipeptide l-Ala1-d-iGlu2-l-Lys3-d-Ala4-d-Lac5. The FemXWv aminoacyl transferase adds the first residue of the side chain onto this nucleotide precursor. Synthesis of the subunit proceeds by the transfer of the phospho-MurNAc-pentadepsipeptide moiety of UDP-MurNAc-pentadepsipeptide to the C55 lipid carrier undecaprenyl phosphate to form lipid intermediate I (undecaprenyl-PP-MurNAc-pentadepsipeptide or lipid I). The addition of GlcNAc to lipid I leads to lipid intermediate II [undecaprenyl-PP-MurNAc-(pentadepsipeptide)GlcNAc] or lipid II. The second and third residues of the l-Ala-l-Ser and l-Ala-l-Ser-l-Ala side chains are added to the lipid intermediates by unknown Fem transferases. The α carboxyl of d-iGlu2 is amidated in mature peptidoglycan (d-iGln2). The insets indicate the relative abundance of precursors and muropeptides, which was determined by the absorbance at 260 and 195 nm, respectively.