Activation of phospholipase C beta 2 by the alpha and beta gamma subunits of trimeric GTP-binding protein
Cotransfection assays were used to show that the members of the GTP-binding protein Gq class of alpha subunits could activate phospholipase C (PLC) beta 2. Similar experiments also demonstrated that G beta 1 gamma 1, G beta 1 gamma 5, and G beta 2 gamma 5 could activate the beta 2 isoform of PLC but not the beta 1 isoform, while G beta 2 gamma 1 did not activate PLC beta 2. To determine which portions of PLC beta 2 are required for activation by G beta gamma or G alpha, a number of PLC beta 2 deletion mutants and chimeras composed of various portions of PLC beta 1 and PLC beta 2 were prepared. We identified the N-terminal segment of PLC beta 2 with amino acid sequence extending to the end of the Y box as the region required for activation by G beta gamma and the C-terminal region as the segment containing amino acid sequences required for activation by G alpha. Furthermore, we found that coexpression of G alpha 16 and G beta 1 gamma 1 but not G beta 1 gamma 5 in COS-7 cells was able to synergistically activate recombinant PLC beta 2. We suggest that G alpha 16 may act together with free G beta 1 gamma 1 to activate PLC beta 2, while G alpha 16 may form heterotrimeric complexes with G beta 1 gamma 5 and be stabilized in an inactive form. We conclude that the regions of PLC beta 2 required for activation by G beta gamma and G alpha are physically separate and that the nature of the G beta subunit may play a role in determining the relative specificity of the G beta gamma complex for effector activation while the nature of the G gamma subunit isoform may be important for determining the affinity of the G beta gamma complex for specific G alpha proteins.
Additional Information© 1993 by the National Academy of Sciences. Contributed by Melvin I. Simon, March 10, 1993. 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.
Published - WUDpnas93.pdf