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Elizabeth Huh, Sergey A Vishnivetskiy, Vsevolod V Gurevich; The role of the finger loop in rhodopsin binding by arrestin-1. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1522.
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© ARVO (1962-2015); The Authors (2016-present)
Determine the role of individual residues in the arrestin finger loop in rhodopsin binding.
Point mutations of individual residues in bovine arrestin-1 were introduced on the background of wild type arrestin-1 and its "enhanced" phosphorylation-independent truncated (1-378) mutant. Functional effects of these mutations were tested in direct binding assay using radiolabeled proteins produced in cell-free translation.
The majority of mutations cause moderate reduction of the binding to activated phophorylated rhodopsin (P-Rh*), which are less than 25%. Only mutations of Arg66, Arg81, and the deletion of Gly76 had greater negative effect. Apparently, unperturbed arrestin-1 interactions with the rhodopsin-attached phosphates prevented greater loss of binding. In contrast, virtually all mutations reduced to a much greater extent the binding of enhanced (1-378) mutant to unphosphorylated activated rhodopsin (Rh*) (this mutant demonstrates high binding to this form of rhodopsin). Some mutations (the deletions of Gly76 and Gly68) caused the loss of up to 90% of Rh* binding. Thus, the finger loop binds unphosphorylated rhodopsin elements, so that the effects of mutations are greater when the interactions with the phosphates on rhodopsin cannot compensate.
In the structure of the arrestin-rhodopsin complex, the finger loop of arrestin-1 inserts itself into the cavity between transmembrane helices that opens upon rhodopsin activation. The structure suggests that the finger loop serves as the "activation sensor" of arrestin-1. In agreement with this hypothesis, finger loop mutations affect arrestin-1 interactions with Rh* much more dramatically than its binding to P-Rh*.
This is a 2020 ARVO Annual Meeting abstract.
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