FIGURE 3.

Proposed three-dimensional structure of Te-PixJ(Cyc-GAF). A, ribbon model of the structure based on alignment of Te-PixJ(Cyc-GAF) with SyB-Cph1(GAF) and threaded using SWISS-MODEL into the three-dimensional structure of SyB-Cph1(GAF) (PDB ID code 2K2N (8)). PCB is shown in cyan, the three Te-PixJ(GAF) cysteines (Cys-522, Cys-555, and Cys-494) are shown in yellow, Asp-492 is shown in green, and Arg-507 is shown in magenta with its potential salt bridges to the PCB B-ring propionate side chain indicated by the dashed lines. B, top view of the bilin and nearby amino acids. The A–D pyrrole rings are indicated. C, schematic representation of the proposed PVB-type chromophore linked via a double thioether linkage between Cys-494 and Cys-522 and the C5 and C3¹ carbons, respectively.