Three-dimensional structure of B. subtilis PRPP synthase. Three-dimensional structure of B. subtilis PRPP synthase. (A) Monomer drawn on the basis of the SO42− PRPP synthase structure (PDB code 1dkr) (49). The N-terminal domain is at the top. Shown are the five-stranded parallel β-sheets (red), helices (blue), flag region (green), regulatory flexible (RF) loop, the ribose 5-phosphate (R5P) loop, and the PP loop (yellow). The unresolved catalytic flexible (CF) loop is shown as a dotted line. (B) Bent and parallel dimers drawn on the basis of the Cd2+ PRPP synthase structure (PDB code 1ibs) (50). Subunit A is colored similar to the monomer in panel A. Shown are the Cd2+ (black), AMP of the active site (red), and sulfate bound at the position of the phosphate moiety of ribose 5-phosphate and at the position of the α-phosphate of ADP of the allosteric site (red). (C) Hexameric propeller structure drawn on the basis of the mADP PRPP synthase structure (PDB code 1dku) (49). Subunit A (as well as subunits C and E) are colored as described for the monomer in panel A. Shown are the positions of the methylene ADP moieties (red) and methylene ADP molecules (green), both modeled to only AMP, of the ATP binding sites and the allosteric sites, respectively. Bjarne Hove-Jensen et al. Microbiol. Mol. Biol. Rev. 2017; doi:10.1128/MMBR.00040-16