Figure 5. RGS4 is allosterically modulated by phospholipids in single turnover hydrolysis assays.
Phosphatidyl inositol triphosphate (PIP3) modulates RGS4 activity though an allosteric “B” site, described previously (Ishii and Kurachi, 2004; Tu and Wilkie, 2004). In single turnover assays, inclusion of phospholipid vesicles containing PIP3, but not phosphatidyl choline (PC) only, inhibits RGS4 GAP activity. Similar reversal of RGS4-mediated GTP hydrolysis acceleration would be expected for an inhibitory compound.