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TI-II: COUNCIL FOR TOBACCO RRSRARCII-U.S.A., INC. Memorandum To: Dr. J.F.Glenn and Staff From: D.H.Ford Re: Site visit with Dr. S. Lanier, Mass. General Hospital, Boston, May8, 1990. Grant No. 2233R2 entitle4olecular characterization of Alpha2- Adrenergic Receptors." Site visitors: D.H.Ford and D. Stone. Goal:To determine the molecular characterization of the alpha2- adrenergic receptor in relation to its heterogeneity in different tissues and species He plans to illustrate such differences by an examination of siructure, protein chemistry and function and finally by utilizing the tools of molecular genetics. Results: See his latest progress report and list of publications for a detailed description. Briefly; he believes that there is a super-gene family which codes for a variety of similar, but morpho- logically and perhaps functionaly different alpha2-adrenergic receptors. The genes for these difference receptor isoforms appear to be localized on chromosomes 4 and 10. Currently, he has been able to clone 4 different isoforms. Diagram of basic receptor structure 91yCosy),atIw• 517es McMS Ra-v b" Coa ic potcnf#.n! Cr-pvr04e"" b"Q!1n5 SIA#0 In this general structure, he has noted that the NH2 end (extracell- ular) may or may not be glycosylated and that the third and largest intracellular loop is the most variable in amino acid sequence and probably the site at which activation of a G-protein occurs. Based on the binding affinities of various ligands (rauwolscine, prazosin and oxymetazoline), there appear to be different isoforms of the receptor in calf spleen, human platelet, neonatal rat lung and rat brain. Further, binding affinities differ between rat and human. A1so,Areceptor in the neonatal rat lung is not glycosylated and is not present in the adult lung. In addition, there appears to be some heterogeneity in the membrane spanning portions of the receptors, which is of interest in that with other receptors, the membrane spanning portions demonstrate considerable homogeneity. He now concludes that there will be considerable specificity as to receptor type (there may be yet other variants), which may also vary as to the G-proteins and functional response . He is planning to transfect his four isoform subtypes into different cell phenotypes to analyze receptor-G protein interaction and functional capacity. This is indeed a very interesting and exciting investigation directed toward how heterogeneity in receptors may influence the response of various cell types. DHF