Surface plasmon resonance-based Gα-binding assays analyzing the inhibitory properties of CCG-4986 on wildtype RGS4 (A), RGS8 (B), RGS16 (C), and indicated cysteine mutants of RGS4 (panels D-F). 6000 resonance units (RU) of biotin-Gαi1 protein was immobilized on a streptavidin biosensor surface. A 200 μl aliquot of 5 μM RGS protein, previously incubated with either DMSO vehicle (black), CCG-4986 (gray), or DTT-reduced CCG-4986 (dotted gray), was injected at 20 μl/min (0 to 600 seconds) with a follow-up 200 seconds of dissociation time in running buffer only (600 to 800 seconds).