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J. Biol. Chem., Vol. 283, Issue 44, 30015-30024, October 31, 2008

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Activation-dependent Hindrance of Photoreceptor G Protein Diffusion by Lipid Microdomains^*

Qiong Wang, Xue Zhang, Li Zhang, Feng He, Guowei Zhang, Milan Jamrich^¶, and Theodore G. Wensel¹

From the Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Program in Developmental Biology, and ^¶Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030

The dynamics of G protein-mediated signal transduction depend on the two-dimensional diffusion of membrane-bound G proteins and receptors, which has been suggested to be rate-limiting for vertebrate phototransduction, a highly amplified G protein-coupled signaling pathway. Using fluorescence recovery after photobleaching (FRAP), we measured the diffusion of the G protein transducin -subunit (G_t) and the G protein-coupled receptor rhodopsin on disk membranes of living rod photoreceptors from transgenic Xenopus laevis. Treatment with either methyl-β-cyclodextrin or filipin III to disrupt cholesterol-containing lipid microdomains dramatically accelerated diffusion of G_t in its GTP-bound state and of the rhodopsin-Gβ_t complex but not of rhodopsin or inactive GDP-bound Gβ. These results imply an activity-dependent sequestration of G proteins into cholesterol-dependent lipid microdomains, which limits diffusion and exclude the majority of free rhodopsin and the free G protein heterotrimer. Our data offer a novel demonstration of lipid microdomains in the internal membranes of living sensory neurons.

Received for publication, May 22, 2008 , and in revised form, July 23, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grants R01-EY07981 and R01-EY12505 from NEI. This work was also supported by Welch Foundation Grant Q0035. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Tel.: 713-798-6994; Fax: 713-798-1625; E-mail: twensel{at}bcm.edu.

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