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W. M. Cleghorn, M. Kim, N. Van Eps, S. A. Vishnivetskiy, S. M. Hanson, V. V. Gurevich, W. L. Hubbell; A Site-Directed Spin Labeling Study of the Conformation of Free and Rhodopsin-Bound Arrestin. Invest. Ophthalmol. Vis. Sci. 2008;49(13):161.
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To elucidate conformational changes in rod arrestin induced by its binding to light-activated phosphorylated rhodopsin (P-Rh*).
Rod arrestin forms tetramers at physiological concentrations. To explore the structure of free (monomer in the solution tetramer) and rhodopsin-bound arrestin, pairs of spin labels were introduced in the molecule. Distances between the pairs were determined by DEER spectroscopy to provide global structural constraints.
We have previously shown that that the structure of the crystal and solution tetramer is different, that only monomeric arrestin binds to P-Rh*, and that arrestin binds individual rhodopsin molecules. The arrestin crystal structure reveals a tetramer in which the monomers have different conformations in flexible regions of the molecule, including the "finger loop" involved in P-Rh* binding. The set from which pairs were selected are shown in the figure, and include sites in both the N- and C-domains.
Distance data are consistent with the D chain conformation seen in the crystal structure tetramer in which the finger loop is in a "bent over", rather than extended, conformation. Pairs involving residue 344 show broad distance distributions indicating plasticity of the host loop. Upon binding to P-Rh*, the pattern of observed distance changes suggests that the structure of the cores of both N- and C-domains remains essentially unchanged, but that specific rearrangements of the finger loop and an adjacent loop containing residue 139 take place.
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