A, the superposition of the ligands (GlcN)5 and (GlcN)6 in the active cleft of OfChtI-CAD. (GlcN)5 and (GlcN)6 are shown as sticks with yellow and cyan carbon atoms, respectively. The catalytic residue Glu148 in two complex structures is labeled and shown as sticks with green carbon atoms. The numbers indicate the subsite to which the GlcN residue is bound. Hydrogen bonds between Glu148 and the ligands are drawn as a dashed line. B, superposition of the inhibitor (GlcN)5 and the substrate (GlcNAc)2/3 (PDB entry 3WL1) in the substrate-binding cleft of OfChtI-CAD. (GlcN)5 and (GlcNAc)2/3 are shown as sticks with yellow and blue carbon atoms, respectively. The catalytic Glu148 and Phe309 in the structures in complex with (GlcN)5 and (GlcNAc)2/3 are labeled and shown as sticks with green and pink carbon atoms, respectively. The numbers indicate the subsite to which the GlcN and GlcNAc residue is bound. Hydrogen bonds between Glu148 and the ligands are drawn as dashed lines.