ROP5 inhibits IRGa6 GTPase activity. The active sites of IRGa6-GDP (A) and ROP5-IRGa6-GDP (B) are shown with residues that coordinate GDP, associated waters, and Mg2+. C, 20 μm IRGa6 was incubated with GTP in either the presence or absence of 150 μm ROP5CI, and released phosphate was measured over time. Error bars, S.D. (n = 3). D, 10 μm IRGa6 was incubated with 2 mm GTP and varying concentrations of either ROP5BI or ROP5CI for 40 min, phosphate release was measured, and activities were normalized to IRGa6 activity without ROP5. Error bars, errors in slope by GraphPad Prism (n = 3 per data point).