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Synergistic activation of phospholipase C-beta3 by Galpha(q) and Gbetagamma describes a simple two-state coincidence detector.

ABSTRACT: Receptors that couple to G(i) and G(q) often interact synergistically in cells to elicit cytosolic Ca(2+) transients that are several-fold higher than the sum of those driven by each receptor alone. Such synergism is commonly assumed to be complex, requiring regulatory interaction between components, multiple pathways, or multiple states of the target protein.We show that cellular G(i)-G(q) synergism derives from direct supra-additive stimulation of phospholipase C-beta3 (PLC-beta3) by G protein subunits Gbetagamma and Galpha(q), the relevant components of the G(i) and G(q) signaling pathways. No additional pathway or proteins are required. Synergism is quantitatively explained by the classical and simple two-state (inactive<-->active) allosteric mechanism. We show generally that synergistic activation of a two-state enzyme reflects enhanced conversion to the active state when both ligands are bound, not merely the enhancement of ligand affinity predicted by positive cooperativity. The two-state mechanism also explains why synergism is unique to PLC-beta3 among the four PLC-beta isoforms and, in general, why one enzyme may respond synergistically to two activators while another does not. Expression of synergism demands that an enzyme display low basal activity in the absence of ligand and becomes significant only when basal activity is

SUBMITTER: Philip F

PROVIDER: S-EPMC2918712 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Synergistic activation of phospholipase C-beta3 by Galpha(q) and Gbetagamma describes a simple two-state coincidence detector.

Philip Finly F Kadamur Ganesh G Silos Rosa González RG Woodson Jimmy J Ross Elliott M EM

Current biology : CB 20100624 15

<h4>Background</h4>Receptors that couple to G(i) and G(q) often interact synergistically in cells to elicit cytosolic Ca(2+) transients that are several-fold higher than the sum of those driven by each receptor alone. Such synergism is commonly assumed to be complex, requiring regulatory interaction between components, multiple pathways, or multiple states of the target protein.<h4>Results</h4>We show that cellular G(i)-G(q) synergism derives from direct supra-additive stimulation of phospholipa ...[more]

PMID: 20579885

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Project description:Phospholipase C-eta2 (PLC-eta2) was recently identified as a novel broadly expressed phosphoinositide-hydrolyzing isozyme [Zhou, Y., et al. (2005) Biochem. J. 391, 667-676; Nakahara, M., et al. (2005) J. Biol. Chem. 280, 29128-29134]. In this study, we investigated the direct regulation of PLC-eta2 by Gbetagamma subunits of heterotrimeric G proteins. Coexpression of PLC-eta2 with Gbeta 1gamma 2, as well as with certain other Gbetagamma dimers, in COS-7 cells resulted in increases in inositol phosphate accumulation. Gbeta 1gamma 2-dependent increases in phosphoinositide hydrolysis also were observed with a truncation mutant of PLC-eta2 that lacks the long alternatively spliced carboxy-terminal domain of the isozyme. To begin to define the enzymatic properties of PLC-eta2 and its potential direct activation by Gbetagamma, a construct of PLC-eta2 encompassing the canonical domains conserved in all PLCs (PH domain through C2 domain) was purified to homogeneity after expression from a baculovirus in insect cells. Enzyme activity of purified PLC-eta2 was quantified after reconstitution with PtdIns(4,5)P 2-containing phospholipid vesicles, and values for K m (14.4 microM) and V max [12.6 micromol min (-1) (mg of protein) (-1)] were similar to activities previously observed with purified PLC-beta or PLC-epsilon isozymes. Moreover, purified Gbeta 1gamma 2 stimulated the activity of purified PLC-eta2 in a concentration-dependent manner similar to that observed with purified PLC-beta2. Activation was dependent on the presence of free Gbeta 1gamma 2 since its sequestration in the presence of Galpha i1 or GRK2-ct reversed Gbeta 1gamma 2-promoted activation. The PH domain of PLC-eta2 is not required for Gbeta 1gamma 2-mediated regulation since a purified fragment encompassing the EF-hand through C2 domains but lacking the PH domain nonetheless was activated by Gbeta 1gamma 2. Taken together, these studies illustrate that PLC-eta2 is a direct downstream effector of Gbetagamma and, therefore, of receptor-activated heterotrimeric G proteins.

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Synergistic activation of phospholipase C-beta3 by Galpha(q) and Gbetagamma describes a simple two-state coincidence detector.

Publications

Synergistic activation of phospholipase C-beta3 by Galpha(q) and Gbetagamma describes a simple two-state coincidence detector.

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