FIGURE 3.

The catalytic center of ChiC. The catalytic glutamate of ChiC exhibits a conformation inconsistent with the putative catalytically active conformation (CAC) (19). A and B, illustrations of these conformations are given showing the conformation found in the ChiC2 crystal structure (A) and showing the putative catalytically active conformation from an MD simulation (B). C, the free energy difference of the catalytic glutamate between the solvent-exposed conformation and the catalytically active complex. A reaction coordinate value of ∼2.5 Å corresponds to the catalytically active complex (19), and a value near 5.5 Å corresponds to the Glu-141 conformation observed in the crystal structure (4AXN). Error bars were obtained by bootstrapping in WHAM. D, superposition of frames from MD simulation of ChiC2 with a GlcNAc₇ ligand bound (see supplemental text for details) illustrating the significant flexibility of Glu-141.