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PMID: 21467038 Published · ppublish English Journal Article Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't

Ric-8B is a GTP-dependent G protein alphas guanine nucleotide exchange factor.

The Journal of biological chemistry ·Vol. 286 ·No. 22 ·2011-06-03 ·Pages 19932-42

Chan P, Gabay M, Wright FA, Tall GG

Abstract

ric-8 (resistance to inhibitors of cholinesterase 8) genes have positive roles in variegated G protein signaling pathways, including Gα(q) and Gα(s) regulation of neurotransmission, Gα(i)-dependent mitotic spindle positioning during (asymmetric) cell division, and Gα(olf)-dependent odorant receptor signaling. Mammalian Ric-8 activities are partitioned between two genes, ric-8A and ric-8B. Ric-8A is a guanine nucleotide exchange factor (GEF) for Gα(i)/α(q)/α(12/13) subunits. Ric-8B potentiated G(s) signaling presumably as a Gα(s)-class GEF activator, but no demonstration has shown Ric-8B GEF activity. Here, two Ric-8B isoforms were purified and found to be Gα subunit GDP release factor/GEFs. In HeLa cells, full-length Ric-8B (Ric-8BFL) bound endogenously expressed Gα(s) and lesser amounts of Gα(q) and Gα(13). Ric-8BFL stimulated guanosine 5'-3-O-(thio)triphosphate (GTPγS) binding to these subunits and Gα(olf), whereas the Ric-8BΔ9 isoform stimulated Gα(s short) GTPγS binding only. Michaelis-Menten experiments showed that Ric-8BFL elevated the V(max) of Gα(s) steady state GTP hydrolysis and the apparent K(m) values of GTP binding to Gα(s) from ∼385 nm to an estimated value of ∼42 μM. Directionality of the Ric-8BFL-catalyzed Gα(s) exchange reaction was GTP-dependent. At sub-K(m) GTP, Ric-BFL was inhibitory to exchange despite being a rapid GDP release accelerator. Ric-8BFL binds nucleotide-free Gα(s) tightly, and near-K(m) GTP levels were required to dissociate the Ric-8B·Gα nucleotide-free intermediate to release free Ric-8B and Gα-GTP. Ric-8BFL-catalyzed nucleotide exchange probably proceeds in the forward direction to produce Gα-GTP in cells.

MeSH Terms
Animals Catalysis Cell Line GTP-Binding Protein alpha Subunits/genetics,metabolism Guanine Nucleotide Exchange Factors/genetics,metabolism Guanosine Triphosphate/genetics,metabolism Mice Nuclear Proteins/genetics,metabolism Protein Isoforms Rats
Chemicals
GTP-Binding Protein alpha Subunits Guanine Nucleotide Exchange Factors Nuclear Proteins Protein Isoforms Ric8a protein, mouse Ric8b protein, mouse Guanosine Triphosphate
Authors & Affiliations
4 authors, click to expand affiliations / ORCID
Chan PuiYee
Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
Gabay Meital
Wright Forrest A
Tall Gregory G
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Article Info
Journal
The Journal of biological chemistry
Abbr.
J Biol Chem
ISSN
1083-351X
DOI
10.1074/jbc.M110.163675
Published
2011-06-03
Epub
2011-00-05
Pages
19932-42
Language
English
Region
United States
NLM ID
2985121R
PMCID
PMC3103368
Subset
IM
Grants
NIGMS NIH HHS · R01 GM088242 · United States
NIDA NIH HHS · T32 DA007232 · United States
NIDA NIH HHS · T32 DA07232 · United States
NIGMS NIH HHS · GM088242 · United States
External Links
PubMed source DOI: 10.1074/jbc.M110.163675 PMC Full Text View journal details
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