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Ric‐8B is a guanine nucleotide exchange factor for G alpha q, G alpha 13, and G alpha s and regulates G alpha s catalysis by a unique mechanism
Author(s) -
Chan PuiYee,
Gabay Meital,
Wright Forrest A,
Tall Gregory G
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.lb476
Subject(s) - gtp' , g protein , gtpase , guanine nucleotide exchange factor , nucleotide , g alpha subunit , gtp binding protein regulators , chemistry , stereochemistry , guanine , protein subunit , biochemistry , receptor , enzyme , gene
Ric‐8A is a non‐receptor GEF for a subset of G protein alpha subunits. Ric‐8B was discovered as a Gαs/Gαq interacting protein and through homology to Ric‐8A has been suggested to be a GEF for these subunits. Here we show in cells and in vitro the complete profile of Ric‐8 protein interactions with representatives of the four G protein alpha subunit classes. Ric‐8BFL (full length) binds Gαq = Gαs > Gα13 ⋙ Gαi, Ric‐8BΔ9 binds Gαs exclusively, and Ric‐8A binds Gαi = Gαq = Gα13. In all cases, but to varying degrees Ric‐8 proteins stimulated GTPγS binding to the G alpha subunits that each bound. Ric‐8BFL stimulated Gαq GTPγS binding and steady state GTP hydrolysis (GTPase). For Gαs, Ric‐8BFL and Ric‐8BΔ9 promoted very rapid GDP release, but delayed the rate at which the open form of Gαs bound GTPγS, although the overall rate of Gαs GTPγS binding was enhanced slightly above the intrinsic rate. Ric‐8BFL, but not Ric‐8BΔ9 also remained bound to Gαs:GTPγS after nucleotide exchange (neither bound Gαq‐GTP). The kinetics of Gαs single turnover GTPase were unaltered by Ric‐8BFL or Ric‐8BΔ9. However, Ric‐8BFL uniquely promoted Gαs futile nucleotide exchange of GTPγS for GTPγS. These collective observations explain in part, the finding that Ric‐8BFL potently inhibited Gαs steady state GTPase activity (overall catalysis), despite being a GEF for Gαs. This work was supported by NIH grant R01GM088242 to G.G.T., and NIDA grant T32 DA07232 to P.C.