In this past year we have succeeded in a number of new initiatives designed to extend our understanding of the molecular interactions of G-proteins and receptors. First, we have confirmed the utility of the baculovirus insect cell system for the expression of functionally active recombinant receptors using rat 5HT2C receptor DNA. Analysis of the properties of the 5HT2C receptor by reconstitution in situ in Sf9 membranes has revealed a previously undescribed basal activity of the receptor and inverse agonist activity of several classical 5HT antagonist compounds. We have also developed procedures for removing the covalent retinal from bovine rhodopsin and subsequent activation of opsin by retinal analogs in order to exploit this as a model for ligand-operated receptors. Opsin also displays a basal activation which is suppressed by cis-retinals in the dark. Using the known structure of rhodopsins, we have modeled the retinal binding site of bovine rhodopsin and designed peptide structures as antagonists of retinal binding. This same model when applied to the 5HT2C receptor designed a distinct set of peptide structures which specifically occupy the 5HT binding site one of which was an agonist of the receptor. Lastly, we have succeeded in applying the novel biophysical approach of surface plasmon resonance to the examination of the protein-protein interactions of G-protein subunits and rhodopsin. The combination of recombinant expression of distinct molecular structures (and mutations) with in vitro biochemical and biophysical analyses should allow us to develop a molecular level description of receptor-G-protein coupling.
