FIGURE 6.

Structural perturbations in the hydrophobic loop. a, the occluding 396 loop position, when in complex with Neu5Ac2en, is shown in yellow (PDB code 4YW0). The nonoccluding loop position, in the unbound active site of the apo-structure, is shown in purple (PDB code 4YZ1). The distance between the Phe-396 Cα carbons in the two conformations is 2.1 Å. Neu5Ac2en is shown in green. Spheres represent the favorable hydrophobic interactions between Phe-396 and Neu5Ac2en. b and c, a solvent-accessible surface has been applied to the nonconstricted and constricted conformations, respectively. The position of the Phe-396 residue is highlighted by a light green surface.