D-Alanyl-D-alanine terminus of peptidoglycan precursor (D-Ala-D-Ala terminus)

The D-Alanyl-D-alanine terminus of peptidoglycan precursor is a critical chemical motif present at the end of the peptide stem of Lipid II and other cell wall precursors in bacteria. During cell wall synthesis, the pentapeptide precursor containing D-Ala-D-Ala is extended and cross-linked to form a robust peptidoglycan sacculus, essential for bacterial survival, morphology, and protection from osmotic pressure. The D-Ala-D-Ala dipeptide is synthesized in the cytoplasm via D-Ala-D-Ala ligase and incorporated into the precursor, which is shuttled to the membrane and polymerized. Clinically important antibiotics, such as glycopeptides (vancomycin, teicoplanin), exert their action by binding to this terminus, preventing transpeptidase-mediated cross-linking and causing bacterial death. Resistance arises when bacteria enzymatically alter the terminus, converting it to D-Ala-D-Lac or D-Ala-D-Ser, thereby reducing drug affinity and leading to therapeutic failure. Targeting the D-Ala-D-Ala motif has proven to be a fundamentally selective and broadly effective strategy for combating bacterial infections.

Other names

D-Ala-D-Ala motifD-alanyl-D-alanine moietyPeptidoglycan pentapeptide terminusMuramyl pentapeptide D-Ala-D-AlaLipid II D-Ala-D-Ala-terminated precursor

Glycopeptide antibiotics (e.g. vancomycin) bind directly and non-covalently to the D-Ala-D-Ala terminus, blocking the action of transpeptidases and transglycosylases, thereby preventing cross-linking and polymerization of peptidoglycan and leading to bacterial cell death. β-lactam antibiotics mimic the D-Ala-D-Ala structure and compete for transpeptidase active sites, inhibiting cross-linking of the cell wall. D-cycloserine inhibits D-Ala-D-Ala ligase, reducing synthesis of the terminus.