Structure and function of a new purinergic receptor

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In 1996, we found a unique adenosine-binding protein, termed as P3LP, which is sensitive not only to adenosine but also to ATP in rat brain membranes. Because properties of P3LP seems to be similar to presumed P3 purinergic receptors, the structure and properties of P3LP have been extensively investigated in this project. First, we developed a specific ligand for P3LP in order to determine the content of P3LP in various tissues and cells and also for the functional assays. As NECA, a non-specific adenosine receptor ligand, was found to bind to P3LP, various derivatives of NECA were synthesized for the screening of P3LP ligand. One of the compounds tested, 9-(6,7-dideoxy-β-D-allo-hept-5-ynofuranosyl) adenine(HAK2701) was found to be a potent ligand for P3LP.Essentially no binding activity was detected with other adenosine receptors. A relativelysimple assay method for P3LP was then developed using HAK2701 as the specific ligand. In the functional studies, HAK2701 was found to facilitate the release of noradrenaline in the rabbit ear artery where the presence of P3 receptor has been reported. This result suggests that HAK2701 may be a potent and selective a agonist for P3 receptor. From the detailed ligand pharmacology of P3LP, it was found that the specificity of P3LP seems to be the hybrid of A1 adenosine receptor and P2Y1 receptor. We therefore tried to form heterodimer between A1 adenosine receptor and P2Y1 receptor that shows a hybrid phamacology by transfection of each cDNA into HEK293T cells. The oligomeric association between these two receptors was shown by co-immunoprecipitation experiments. Functionally, the co-transfected cells revealed A1 adenosine receptor activity with P2Y_1R-like agonistic pharmacology. These studies strongly suggest P3 purinergic receptor or P3LP is really a hybrid purinoceptor between purinergic receptors.