<p>This entry represents the C-terminal, catalytic domain of the D-alanine--D-alanine ligase enzyme <db_xref db="EC" dbkey="6.3.2.4"/>. D-Alanine is one of the central molecules of the cross-linking step of peptidoglycan assembly. There are three enzymes involved in the D-alanine branch of peptidoglycan biosynthesis: the pyridoxal phosphate-dependent D-alanine racemase (Alr), the ATP-dependent D-alanine: D-alanine ligase (Ddl), and the ATP-dependent D-alanine:D-alanine-adding enzyme (MurF) [<cite idref="PUB00014287"/>].</p>