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SA Vishnivetskiy, VV Gurevich, MM Hosey; Two Elements In The Two Domains of The Arrestin Molecule Determine Its Receptor Specificity . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1393.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To elucidate the structural basis for arrestins' receptor specificity. Four cloned arrestin proteins participate in homologous desensitization of hundreds of G protein-coupled receptors. Although the receptor specificity of the two non-visual arrestins is not known, the specificity of rod and cone arrestins for their respective pigments is inferred from their selective expression in these two types of photoreceptor cells. Recently we found that cone arrestin has a 50-fold lower affinity for phosphorylated light-activated rhodopsin (P-Rh*) than rod visual arrestin (VA). The difference in affinity of bovine and salamander VA for P-Rh* of the corresponding vs the other species is of similar magnitude. Methods: Experimentally the preference of VA for P-Rh* and that of beta-arrestin (BA) for agonist-activated phosphorylated m2 muscarinic cholinergic receptor (P-m2*) can be measured in the direct binding assay. Each arrestin demonstrates about 6-fold higher binding to the preferred receptor than the other arrestin. To elucidate the part of arrestin responsible for receptor specificity, we constructed a series of VA-based chimeras containing 12 different elements of the BA N-domain and 8 elements of its C-domain. These proteins were expressed in cell-free translation in radiolabeled form and tested in the direct binding assay with both receptors. Results: Incorporation of the N-domain BA element 46 to 86 (EI) in place of the homologous part of VA yields a chimera with BA-like high binding to P-m2* and low binding to P-Rh*. Another chimera, with C-domain BA element 237-293 (EII), demonstrates a similar phenotype. According to the crystal structure, EI includes beta-strands V and VI and adjacent loops. Only 15 residues in this region are different in VA and BA, and just 4 of these are non-conservative substitutions. EII includes beta-strands XVI, XVII and adjacent loops with highly variable structure and has 16 non-conservative substitutions. Conclusion: Only a few non-contiguous residues localized in both the N- and C-domains of arrestin proteins are largely responsible for their receptor specificity. Point mutations in EI and EII will help us elucidate the role of individual arrestin residues in receptor recognition. Support: NIH grants EY11500 and GM63097 (V.V.G.)
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