Figure 1. Model of the substrate-binding site of WbpP and other C4 epimerases.

(a) The substrate-binding pocket is represented by an hexagon. Three of the six sides are made of the three conserved Ser¹⁴² (yellow), Tyr¹⁶⁶ (blue) and Asn¹⁹⁵ (orange) residues in WbpP. The three other sides are made of Gly¹⁰² (red), Ala²⁰⁹ (purple) and Ser³⁰⁶ (green). (b) The corresponding residues found in other homologues are indicated, and a selection of mutations tested in the present paper is highlighted. The UDP-GlcNAc and UDP-GalNAc bound in catalytically productive conformations are represented by a solid line. The role of water molecules is signified by spheres. Adapted from [4] with permission. © 2004 American Society for Biochemistry and Molecular Biology.