Regulation of deactivation of photoreceptor G protein by its target enzyme and cGMP.

Published

Journal Article

The photoreceptor G protein, transducin, is one of the class of heterotrimeric G proteins that mediates between membrane receptors and intracellular enzymes or ion channels. Light-activated rhodopsin catalyses the exchange of GDP for GTP on multiple transducin molecules. Activated transducin then stimulates cyclic GMP phosphodiesterase by releasing an inhibitory action of the phosphodiesterase gamma-subunits. This leads to a decrease in cGMP levels in the rod, and closure of plasma membrane cationic channels gated by cGMP. In this and other systems, turn-off of the response requires the GTP bound to G protein to be hydrolysed by an intrinsic GTPase activity. Here we report that the interaction of transducin with cGMP phosphodiesterase, specifically with its gamma-subunits, accelerates GTPase activity by several fold. Thus the gamma-subunits of the phosphodiesterase serve a function analogous to the GTPase-activating proteins that regulate the class of small GTP-binding proteins. The acceleration can be partially suppressed by cGMP, most probably through the non-catalytic cGMP-binding sites of phosphodiesterase alpha and beta-subunits. This cGMP regulation may function in light-adaptation of the photo-response as a negative feedback that decreases the lifetime of activated cGMP phosphodiesterase as light causes decreases in cytoplasmic cGMP.

Full Text

Duke Authors

Cited Authors

  • Arshavsky VYu, ; Bownds, MD

Published Date

  • June 4, 1992

Published In

Volume / Issue

  • 357 / 6377

Start / End Page

  • 416 - 417

PubMed ID

  • 1317509

Pubmed Central ID

  • 1317509

International Standard Serial Number (ISSN)

  • 0028-0836

Digital Object Identifier (DOI)

  • 10.1038/357416a0

Language

  • eng

Conference Location

  • England