Abstract
Purpose :
Determine the conformational flexibility of the arrestin-rhodopsin complex.
Methods :
Distance measurements by double electron-electron resonance (DEER) between selected points in arrestin-1 and rhodopsin. Purified single-cysteine mutants of enhanced phosphorylation-independent arrestin and expressed and purified rhodopsin are chemically modified with nitroxide spin label, allowed to bind, and the distances are then measured by pulse EPR technique DEER.
Results :
For each pair of points in arrestin and rhodopsin we detected multiple distances, some of which match the crystal structure of the arrestin-receptor complex. The presence of three to four distinct distances detected by DEER in each case suggests that alternative shapes of this complex exist, which are not captured by crystallization. These data are consistent with the flexibility of rhodopsin-bound arrestin earlier detected using biophysical methods EPR and NMR that reveal protein dynamics. Modeling of the complex using the conformations of light-activated rhodopsin and rhodopsin-bound arrestin identified by X-ray crystallography suggests that the orientation of the two proteins in the complex relative to each other can be different. The data also suggest that active receptor-bound arrestin can assume several distinct conformations.
Conclusions :
The complex of arrestin-1 bound visual pigment rhodopsin exists in several distinct conformations, only one of which is captured by the crystal structure. As rhodopsin is a prototypical class A G protein-coupled receptor, these data reveal the structural basis of functional diversity of the arrestin-receptor complexes.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.