Fig. 2. Structure of the E. coli PAPS reductase–mutant Trx1 mixed disulfide complex. (A) Secondary structure representation of the complex, top: PR (CysH), bottom: Trx1. (B) Surfaces in atomic type coloring after rotation of PR by 90° backwards and Trx1 by 90° to the front. The arrow points to the two cysteinyl sulfur atoms that form the intermediate mixed disulfide. (C) The contact surfaces marked in blue. (D) The electrostatic surface potentials (from red = –4 to blue = +4 kT per e, using atomic partial charges) mapped to the surface and highlighting the contact surfaces and some specifically interacting amino acid site chains. All pictures and data were computed using the DeepView/Swiss-PDB Viewer 4.1 with PDB accession number ; 2o8v.29.