NacetylmuramoylLalanyl

N-acetylmuramoyl-L-alanine, commonly abbreviated NAM-L-Ala, is a building block of bacterial peptidoglycan. It consists of the N-acetylmuramic acid (MurNAc) sugar moiety linked to the amino acid L-alanine via the MurNAc lactyl group. In the peptidoglycan repeating unit, NAM-L-Ala represents the first residue of the stem peptide attached to MurNAc, from which the rest of the stem peptide extends, typically including D-glutamate and a third amino acid (such as meso-diaminopimelic acid or L-lysine) followed by D-alanine–D-alanine in many bacteria.

Biosynthesis and role in cell wall assembly: NAM-L-Ala is produced in the bacterial cytoplasm as part of the UDP-MurNAc-pentapeptide precursor. The MurC ligase adds L-alanine to UDP-N-acetylmuramic acid (UDP-MurNAc), after which MurD, MurE, and MurF sequentially add the remaining amino acids to form UDP-MurNAc-pentapeptide. This precursoris then attached to a sugar backbone to form the mature peptidoglycan precursor, which is transported across the membrane and incorporated into the cell wall. The stem peptide of NAM-L-Ala is ultimately cross-linked to neighboring stems, providing structural integrity to the cell wall.

Biological and clinical relevance: NAM-L-Ala is a fundamental component of bacterial cell walls and is essential for cell viability in many species. Enzymes that synthesize NAM-L-Ala and the downstream peptidoglycan assembly steps are targets of antibiotics that disrupt cell wall synthesis, such as the Mur ligases and penicillin-binding proteins. NAM-L-Ala is thus central to understanding bacterial morphology and antibiotic mechanisms.

See also: MurC/D/E/F enzymes, peptidoglycan, UDP-MurNAc, penicillin-binding proteins.