Fig. 4.

Close-up view of the active-site cleft of wild-type NAL (a) and the E192N variant (b). The backbone is shown as a gray cartoon, and active-site residues are shown as sticks colored by atom type. (c) Wild type and (d) E192N are the same view and show the solvent-accessible surface colored by electrostatic potential (calculated in PyMOL; blue, positive; red, negative) to illustrate the change in surface potential as a result of glutamate-to-asparagine mutation, as well as the position of residue 192 at the entrance to the active-site cleft.