The G Protein β5 Subunit Interacts Selectively with the Gq α Subunit

• Published in: The Journal of biological chemistry 1998-01, Vol.273 (1), p.636
• Main Authors: Julia E. Fletcher, Margaret A. Lindorfer, Joseph M. DeFilippo, Hiroshi Yasuda, Maya Guilmard, James C. Garrison
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.1.636

The diversity in the heterotrimeric G protein α, β, and γ subunits may allow selective protein-protein interactions and provide specificity for signaling pathways. We examined the ability of five α subunits (α i1 , α i2 , α o , α s , and α q ) to associate with three β subunits (β 1 , β 2 , and β 5 ) dimerized to a γ 2 subunit containing an amino-terminal hexahistidine-FLAG affinity tag (γ 2HF ). Sf9 insect cells were used to overexpress the recombinant proteins. The hexahistidine-FLAG sequence does not hinder the function of the β 1 γ 2HF dimer as it can be specifically eluted from an α i1 -agarose column with GDP and AlF 4 − , and purified β 1 γ 2HF dimer stimulates type II adenylyl cyclase. The β 1 γ 2HF and β 2 γ 2HF dimers immobilized on an anti-FLAG affinity column bound all five α subunits tested, whereas the β 5 γ 2HF dimer bound only α q . The ability of other α subunits to compete with the α q subunit for binding to the β 5 γ 2HF dimer was tested. Addition of increasing amounts of purified, recombinant α i1 to the α q in a Sf9 cell extract did not decrease the amount of α q bound to the β 5 γ 2HF column. When G proteins in an extract of brain membranes were activated with GDP and AlF 4 − and deactivated in the presence of equal amounts of the β 1 γ 2HF or β 5 γ 2HF dimers, only α q bound to the β 5 γ 2HF dimer. The α q -β 5 γ 2HF interaction on the column was functional as GDP, and AlF 4 − specifically eluted α q from the column. These results indicate that although the β 1 and β 2 subunits interact with α subunits from the α i , α s , and α q families, the structurally divergent β 5 subunit only interacts with α q .