Fig. 4.

Ac92 active-site and surface properties. (A) The active-site region of Ac92 is shown with the side chain atoms of the CXXC motif in spheres at half their van der Waals radii. The FAD is in orange sticks, and the side chains of residues making key electrostatic interactions (dotted red lines) with the FAD also are shown as sticks. (B) An electrostatic surface representation of the Ac92 dimer is shown with regions of basic potential colored blue (>10 k_BT/e) and acidic regions red (<−10 k_BT/e, where k_B is the Boltzmann constant, T is the absolute temperature, and e is the electron charge). The spring labeled 20 to 25 Å in the top panel represents the variability seen in the distance between the walls of the groove in the Ac92 structure when the P1 and C2 crystal structures were compared. The approximate locations of the Ac92-N and Ac92-C domains and their symmetry-related copies (Ac92-N′ and Ac92-C′) are indicated. In the bottom view, yellow arrows point at the active-site disulfides and approximate the direction from which substrate thiols would approach.