Ubiquitylation of the transducin betagamma subunit complex. Regulation by phosducin.
Journal Article (Journal Article)
G proteins (Galphabetagamma) are essential signaling molecules, which dissociate into Galpha and Gbetagamma upon activation by heptahelical membrane receptors. We have identified the betagamma subunit complex of the photoreceptor-specific G protein, transducin (T), as a target of the ubiquitin-proteasome pathway. Ubiquitylated species of the transducin gamma-subunit (Tgamma) but not the alpha- or beta-subunits were assembled de novo in bovine photoreceptor preparations. In addition, Tgamma was exclusively ubiquitylated when Tbetagamma was dissociated from Talpha. Ubiquitylation of Tbetagamma on Tgamma was selectively catalyzed by human ubiquitin-conjugating enzymes UbcH5 and UbcH7 and was coincident with degradation of the entire Tbetagamma subunit complex in vitro by a mechanism requiring ATP and the proteasome. We also show that Tbetagamma association with phosducin, a photoreceptor-specific protein of unknown physiological function, blocks Tbetagamma ubiquitylation and subsequent degradation. Phosphorylation of phosducin by Ca(2+)/calmodulin-dependent protein kinase II, which inhibits phosducin-Tbetagamma complex formation, completely restored Tbetagamma ubiquitylation and degradation. We conclude that Tbetagamma is a substrate of the ubiquitin-proteasome pathway and suggest that phosducin serves to protect Tbetagamma following the light-dependent dissociation of Talphabetagamma.
Full Text
Duke Authors
Cited Authors
- Obin, M; Lee, BY; Meinke, G; Bohm, A; Lee, RH; Gaudet, R; Hopp, JA; Arshavsky, VY; Willardson, BM; Taylor, A
Published Date
- November 15, 2002
Published In
Volume / Issue
- 277 / 46
Start / End Page
- 44566 - 44575
PubMed ID
- 12215439
International Standard Serial Number (ISSN)
- 0021-9258
Digital Object Identifier (DOI)
- 10.1074/jbc.M205308200
Language
- eng
Conference Location
- United States