The catecholamine dopamine (DA) plays a role in the regulation of cognitive, emotional, and behavioral functions. Abnormalities in its regulation have been implicated in several psychiatric and neurologic disorders. DA exerts it actions at a number of G-protein-coupled receptors (GPCRs), including D2-like and D1-like receptors. Antipsychotic mediations potently inhibit D2-like receptors. DA reuptake by the DA transporter (DAT) is a major mechanism for terminating dopaininergic transmission, and this protein is the molecular target of several psychostimulants, including amphetamine and cocaine. The long-term goals and research objectives of the Javitch laboratory are: a) To understand the structural bases of agonist and antagonist binding and specificity in the DA D2-like receptors and related biogenic amine receptors; b) To determine how agonist binding is transduced into G-protein activation; c) To determine the structural bases of the transport of substrate by the DAT and its inhibition by drugs such as cocaine. In pursuit of these long-term goals, the objectives of the current K02 application include research on the structure, function and regulation of DAT and related bacterial homologs, and D2-like and related GPCRS, as well as training in biophysical and structural approaches to membrane receptor and transporter structure and function. These objectives, which are summaries of the proposed aims of the applicant's four NIH grants, include: 1) To map the interaction surface between D2 receptors in the membrane environment by cross-linking endogenous and substituted cysteines, to assess whether this interface is shared by other aminergic receptors, and to assess the functional effects of cross-linking and the effects of receptor activation on cross-linking; 2) To map residues forming the surface of the DA and cocaine binding sites in DAT; 3) To map the dimer interface in DAT and to assess the functional significance of dimerization; 4) To clone, express, and characterize bacterial homologs of the sodium- and chloride-dependent neurotransmitter transporters, and to assess their suitability for biochemical, spectroscopic and crystallization studies; 5) To pursue molecular modeling studies in both receptor and transporters to help to interpret our experimental studies from a structural perspective. Interactions and collaborations designed to expose the applicant to new methodologies in biophysical and structural biology are also proposed and particularly relevant to objective 4, which represents a new area of research for the applicant.