Bradykinin (BK) has a variety of biological actions such as vasodilation, smooth muscle contraction or relaxation, bronchoconstriction, inflammation, pain and edema. The pathological and physiological effects of bradykinin are mediated through the bradykinin B2 receptor (BKB2R), a G-protein coupled receptor. We are modifying specific amino acids or groups of amino acids in the intracellular face of the BKB2R to determine the motifs involved in the activation of second messengers as well as motifs involved in desensitization, uptake, and resensitization of the receptor. In the course of our work we have produced a BKB2 hybrid receptor much of whose intracellular face has been replaced by the intracellular face of the angiotensin receptor (AT1aR). This hybrid receptor responds to BK by increasing the expression of the connective tissue growth factor (CTGF), a function of the AT1aR but not the BKB2R. Our working hypothesis is that global exchanges in the intracellular face between BKB2R and other unrelated G-protein coupled receptors can result in receptors that respond to BK ligand but signal and desensitize as the donor receptor. The signaling capacity depends on specific motifs generally not originating from one region but a collection of motifs located in separate regions, which are functionally interactive. To test this hypothesis 1) we will continue to create hybrid receptors using global exchanges. Exchanges within each region will be modified to develop an optimally active hybrid receptor. We will focus on a) the AT1aR and b) the cAMP producing EP2R as donors and BKB2R as recipient. 2) We will reverse the processes described above and create a BKB2 functioning receptor responsive to Angiotensin II stimulation. 3) We will continue to investigate in depth, critical regions, critical sequences, critical individual residues, and their interactions within the BKB2R with respect to receptor function and maintenance. A better understanding of structure/function relationships in the receptor and the generation of hybrid receptors responding to BK but taking on the function of another receptor could lead to new therapeutic approaches in dealing with such pathological states as pain, shock, inflammation or hypertension.
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