Neurotransmitter signaling often involves activation of G protein-coupled receptors (GPCRs). Modulation of neurotransmitter receptor signaling is a key therapeutic tool in ameliorating the cognitive pathologies of diseases such as schizophrenia and depression. "Regulator of G-protein signaling" (RGS) proteins are key components of GPCR signaling that act as GTPase-accelerating proteins or "GAPs" for Ga subunits, dramatically increasing their intrinsic GTP hydrolysis activity. In order to advance the utility of RGS proteins as drug discovery targets for cognitive pathologies, the specific aims of this research proposal are to delineate the structural determinants of allosteric modulation of RGS-box GAP activity and to identify small molecule inhibitors and activators of RGS-box GAP activity by computational approaches. Statistical coupling analyses of RGS-box sequences and site identification algorithms applied to known RGS-box structures will guide in silico docking of compounds from commercial and public compound libraries. The activity of compound "hits" identified in these screens will be evaluated using fluorescence- and surface plasmon resonance-based in vitro assays of RGS-box Ga-binding and Ga-GAP activities. Verified modulators of RGS-box GAP activity will then be evaluated in cellular assays of receptor/G-protein/effector function, including receptor-dependent activation of heterotrimer steady-state GTPase activity and of phospholipase C activity. These pursuits should identify proof-of-principle small molecule modulators of RGS protein action that will establish RGS proteins as valid targets for therapeutic intervention in future pharmacotherapy of CNS disorders.