Ubiquitylation of the Transducin Βγ Subunit Complex. Regulation by Phosducin
Author
Obin, Martin
Lee, Bruce Y.
Meinke, Gretchen
Bohm, Andrew
Lee, Rehwa H.
Gaudet, Rachelle
Hopp, Johnathan A.
Arshavsky, Vadim Y.
Willardson, Barry M.
Taylor, Allen
Published Version
https://doi.org/10.1074/jbc.M205308200Metadata
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Obin, Martin, Bruce Y. Lee, Gretchen Meinke, Andrew Bohm, Rehwa H. Lee, Rachelle Gaudet, Johnathan A. Hopp, Vadim Y. Arshavsky, Barry M. Willardson, and Allen Taylor. 2002. “Ubiquitylation of the Transducin Βγ Subunit Complex.” Journal of Biological Chemistry 277 (46): 44566–75. https://doi.org/10.1074/jbc.m205308200.Abstract
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 Ca2+/calmodulin-dependent protein kinase II, which inhibits phosducin-Tbetagamma complex formation, completely restored Toy 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.Terms of Use
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