Selective activation of phospholipase C by recombinant G-protein alpha- and beta gamma-subunits.
Receptor activation of phospholipase C (PLC) via G-proteins occurs by pertussis toxin-sensitive and toxin-insensitive signaling pathways. The alpha-subunits of the Gq family are presumed to mediate the toxin-insensitive pathway, but the nature of the G-proteins mediating the toxin-sensitive pathway is not established. Recently, PLC-beta has been shown to be activated by G-protein beta gamma-subunits of mixed or undefined composition. The relative activities of G-protein subunits that might activate PLC-beta were examined using defined recombinant alpha- and beta gamma-subunits obtained from the baculovirus expression system by reconstituting the purified subunits with purified bovine brain PLC-beta 1 or turkey erythrocyte PLC-beta in unilamellar phospholipid vesicles. Turkey erythrocyte G alpha 11 and recombinant G alpha 11 and G alpha q obtained after expression in Sf9 cells activated both bovine brain PLC-beta 1 and turkey erythrocyte PLC-beta. In contrast, under the same assay conditions, recombinant G alpha i1, G alpha i2, G alpha i3, and G alpha o were without effect on either type of PLC. All types of beta gamma-subunits tested (r beta 1 gamma 2, r beta 1 gamma 3, r beta 2 gamma 2, r beta 2 gamma 3, bovine brain beta gamma or turkey erythrocyte beta gamma) inhibited G alpha 11-mediated activation of PLC, presumably by promotion of formation of inactive heterotrimeric G-protein. All types of beta gamma-subunits also markedly stimulated the activity of turkey erythrocyte PLC-beta but did not activate bovine brain PLC-beta 1. Of the four different beta gamma complexes of defined composition, three stimulated PLC with similar activities whereas beta 2 gamma 3 was less effective. The data suggest that pertussis toxin-sensitive activation of PLC is mediated by the beta gamma-subunits of G-proteins acting on specific phospholipase C isoenzymes.
Boyer
J L
JL
Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill 27599.
Graber
S G
SG
Waldo
G L
GL
Harden
T K
TK
Garrison
J C
JC
D000818:Animals; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004912:Erythrocytes / Q000201:enzymology; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009036:Moths; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D014162:Transfection; D014422:Turkeys; D010738:Type C Phospholipases / Q000378:metabolism*
D007527:Isoenzymes; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins