Purification and characterization of recombinant G16 alpha from Sf9 cells: activation of purified phospholipase C isozymes by G-protein alpha subunits

Creators: Kozasa, Tohru; Hepler, John R.; Smrcka, Alan V.; Simon, Melvin I.; Rhee, Sue Goo; Sternweis, Paul C.; Gilman, Alfred G.

Abstract

A cDNA encoding G16 alpha, the alpha subunit of a heterotrimeric guanine nucleotide-binding protein, was expressed in Sf9 cells using recombinant baculovirus. G16 alpha in membrane extracts of Sf9 cells activated phospholipase C-beta 1 (PLC-beta 1) in the presence of guanosine 5'-[gamma-thio]triphosphate; the system could not be activated by Al3+, Mg2+, and F-. The G16 alpha in the cytosolic fraction of Sf9 cells did not stimulate PLC-beta 1. Concurrent expression of the G-protein beta gamma subunit complex increased the amount of G16 alpha in Sf9 cell membranes. The guanosine 5'-[gamma-thio]triphosphate-activated form of G16 alpha was purified from cholate extracts of membranes from cells expressing G16 alpha, and the G-protein beta 2 and gamma 2 subunits. G16 alpha activated PLC-beta 1, PLC-beta 2, and PLC-beta 3 in a manner essentially indistinguishable from that of Gq alpha. G16 alpha-mediated activation of PLC-beta 1 and PLC-beta 3 greatly exceeded that of PLC-beta 2. G16 alpha did not activate PLC-gamma 1 or PLC-delta 1. Thus, two distantly related members of the Gq alpha family, Gq alpha and G16 alpha, have the same ability to activate the known isoforms of PLC-beta.

Additional Information

© 1993 by the National Academy of Sciences. Contributed by Alfred G. Gilman, July 9, 1993. We thank Linda Hannigan for excellent technical assistance and Stephen Gutowski for preparation of antibodies. This work was supported by National Institutes of Health Grants GM34497, GM31954, and GM34236; American Cancer Society Grant BE30-O; The Perot Family Foundation; The Lucille P. Markey Charitable Trust; The Raymond Willie Chair of Molecular Neuropharmacology; National Research Service Awards GM13569 (to J.R.H.) and GM14489 (to A.V.S.); and a Human Frontier Science Program Organization award (to T.K.). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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