<p> D-alanine--D-alanine ligase (<db_xref db="EC" dbkey="6.3.2.4"/>) is a bacterial enzyme involved in cell-wall biosynthesis. It participates in forming UDP-N-acetylmuramoyl pentapeptide, the peptidoglycan precursor. These enzymes are proteins of 300 to 360 amino acids containing many conserved regions. The N-terminal Gly-rich region could be involved in ATP-binding.</p><p> This family of enzymes represent chromosomal versions of species not specifically resistant to glycopeptide antibiotics such as vancomycin. The mechanism of glycopeptide antibiotic resistance involves the production of D-alanine-D-lactate (VanA and VanB families) or D-alanine-D-serine (VanC). This model attempts to exclude the VanA/VanB and VanC subfamilies while capturing most other D-Ala-D-Ala ligases above the trusted cut-off. However, changes in small numbers of amino acids, as demonstrated crystallographically, can alter specificity. In chlamydial species, this enzyme is found as a fusion protein with UDP-N-acetylmuramate--alanine ligase.</p>