FIGURE 21.

Possible reaction mechanism for the formation of thioether bond catalyzed by QhpD. The active site of QhpD is depicted by a stick model extracted from the modeled QhpD structure (Fig. 15) with the ribbon model of QhpC built by Coot (26) and shown in purple, except for the cross-linked loop structure containing Cys-7–Glu-16 in step vi, which was adopted from the coordinates of the γ subunit (maturated QhpC) in the QHNDH crystal structure. Distances between the two atoms connected by cyan dotted lines are indicated in angstroms (Å). Red and purple curves with an arrowhead show presumed routes of electron transfer. All molecular drawings were generated using PyMOL.