Mammalian Ric-8A (synembryn) is a heterotrimeric Galpha protein guanine nucleotide exchange factor.

The activation of heterotrimeric G proteins is accomplished primarily by the guanine nucleotide exchange activity of ligand-bound G protein-coupled receptors. The existence of nonreceptor guanine nucleotide exchange factors for G proteins has also been postulated. Yeast two-hybrid screens with Galpha(o) and Galpha(s) as baits were performed to identify binding partners ...
of these proteins. Two mammalian homologs of the Caenorhabditis elegans protein Ric-8 were identified in these screens: Ric-8A (Ric-8/synembryn) and Ric-8B. Purification and biochemical characterization of recombinant Ric-8A revealed that it is a potent guanine nucleotide exchange factor for a subset of Galpha proteins including Galpha(q), Galpha(i1), and Galpha(o), but not Galpha(s). The mechanism of Ric-8A-mediated guanine nucleotide exchange was elucidated. Ric-8A interacts with GDP-bound Galpha proteins, stimulates release of GDP, and forms a stable nucleotide-free transition state complex with the Galpha protein; this complex dissociates upon binding of GTP to Galpha.
Mesh Terms:
Animals, Caenorhabditis elegans Proteins, Chromatography, Gel, Cloning, Molecular, Guanine Nucleotide Exchange Factors, Heterotrimeric GTP-Binding Proteins, Molecular Sequence Data, Nuclear Proteins, Rats, Two-Hybrid System Techniques
J. Biol. Chem.
Date: Mar. 07, 2003
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