Fig. 4: Crystal structures of R56A-PaHisGS and R56A-PaATPPRT bound to PRPP:ATP.

a Stick model of the active site of R56A-PaHisGS. b Stick model of the active site of R56A-PaATPPRT. In both panels, oxygen is shown in red, nitrogen in blue, phosphorus in orange, sulphur in yellow, and carbon in either magenta (substrates) or grey (protein). The A56 side chain is contributed by the adjacent PaHisGS subunits. Polar interactions are depicted as dashed lines, and the Mg2+ as a sphere.