Fig. 6

Differential conformations and kinetics of wild-type and D216 ATP-PRT in the presence of l-His or TIH. Cartoon representation highlighting the H-bonds surrounding l-His a and TIH b in their respective crystal structures. The D216 side chain in the TIH-bound ATP-PRT structure could be fitted in two conformations with 0.35 and 0.65 occupancy. Steady-state kinetics of ATP-PRT inhibition by l-His c, and activation by TIH d. WT (black circles), D216 V (red circles) and D216 V + 2 mM l-His (blue circles), error bars indicate the s.d., n = 3. Circles are experimental measurements and lines are the best fit to Eq. 2 (Methods section) for inhibition by l-His and Eq. 4 (Methods section) for activation by TIH. Data for D216 V inhibition by l-His were fit to a linear regression. For WT, an IC ₅₀ for l-His of 22 ± 4 μM and an AC ₅₀ for TIH of 1.5 ± 0.2 mM were obtained. For D216 V, an AC ₅₀ for TIH of 1.7 ± 0.1 mM was obtained, which did not change in the presence of 2 mM l-His, with an AC ₅₀ of 1.5 ± 0.1 mM. l-His (up to 10 mM) did not change D216 V activity and therefore an IC ₅₀ could not be determined