Each rhodopsin molecule binds its own arrestin

doi:10.1073/pnas.0610886104

Each rhodopsin molecule binds its own arrestin

Department of Pharmacology, Vanderbilt University, 2200 Pierce Avenue, PRB, Room 418, Nashville, TN 37232

Communicated by John H. Exton, Vanderbilt University School of Medicine, Nashville, TN, January 4, 2007 (received for review September 19, 2006)

Abstract

Arrestins (Arrs) are ubiquitous regulators of the most numerous family of signaling proteins, G protein-coupled receptors. Two models of the Arr–receptor interaction have been proposed: the binding of one Arr to an individual receptor or to two receptors in a dimer. To determine the binding stoichiometry in vivo, we used rod photoreceptors where rhodopsin (Rh) and Arr are expressed at comparably high levels and where Arr localization in the light is determined by its binding to activated Rh. Genetic manipulation of the expression of both proteins shows that the maximum amount of Arr that moves to the Rh-containing compartment exceeds 80%, but not 100%, of the molar amount of Rh present. In vitro experiments with purified proteins confirm that Arr “saturates” Rh at a 1:1 ratio. Thus, a single Rh molecule is necessary and sufficient to bind Arr. Remarkable structural conservation among receptors and Arrs strongly suggests that all Arr subtypes bind individual molecules of their cognate receptors.

Footnotes

*To whom correspondence should be addressed. E-mail: vsevolod.gurevich{at}vanderbilt.edu
Author contributions: S.M.H. and V.V.G. designed research; S.M.H., E.V.G., S.A.V., M.R.A., X.S., and V.V.G. performed research; S.M.H., E.V.G., S.A.V., M.R.A., X.S., and V.V.G. analyzed data; and S.M.H., E.V.G., and V.V.G. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0610886104/DC1.
Abbreviations:

GPCR,

G protein-coupled receptor;

OS,

outer segment;

Arr,

arrestin;

Rh,

rhodopsin.