Figure 5. Structures of AA and DA substrates in the active site of COD.

A) X-ray structure of the complex COD·AA²⁵. B) Modelled structure with the DA substrate. Ligands are shown as thick lines, metal ion as a green sphere. Only the amino acids interacting with the N-acetyl group at the non-reducing end are shown (as thick lines). The removal of this acetyl group does not alter significantly the interactions map at the active-site, where only one hydrogen-bond with R304 is lost.