Nacetylmuramic

N-acetylmuramic acid, commonly abbreviated MurNAc, is a derivative of muramic acid and a fundamental constituent of bacterial cell wall peptidoglycan. It is a sugar molecule that bears an N-acetyl group and a lactic acid–derived lactyl substituent, the latter serving as the attachment point for a short peptide stem that extends from the bacterial cytoplasm to the cell wall.

In peptidoglycan, MurNAc residues alternate with N-acetylglucosamine (GlcNAc) to form long glycan chains. Each MurNAc carries a short peptide stem that typically includes L-alanine, D-glutamate, and either meso-diaminopimelic acid or L-lysine, often ending with D-alanine residues. Cross-linking between peptide stems, accomplished by penicillin-binding proteins, gives the rigid, mesh-like structure of the cell wall.

Biosynthesis begins in the cytoplasm with the conversion of UDP-N-acetylglucosamine to UDP-N-acetylmuramyl-pentapeptide by Mur enzymes (MurA–MurF). The MurNAc-pentapeptide is then linked to a lipid carrier to form Lipid I and Lipid II, transported across the cytoplasmic membrane, and recycled during peptidoglycan assembly. The sugar-peptide repeats are polymerized by glycosyltransferases and cross-linked by transpeptidases.

MurNAc-containing peptidoglycan is unique to bacteria, making its biosynthetic pathway a target for antibiotics. Inhibitors such as fosfomycin disrupt MurA; beta-lactam antibiotics inhibit penicillin-binding proteins that catalyze cross-linking.