PLC beta 3 Gq

Introduction

Phospholipase C (PLC) catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate [IP2] to the second messengers inositol 1,4,5-trisphosphate [IP3] and diacylglycerol [DAG] in an essential step for the physiological action of many hormones, neurotransmitters, growth factors, and other extracellular stimuli. These cascades use signaling complexes consisting of G alpha subunits of the Gq family of heterotrimeric guanine nucleotide–binding proteins (G proteins) and PLC-beta isozymes (β1-4). Agonist-stimulated receptors increase exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) on Gαq. GTP-bound Gαq engages and activates PLC- β3, and PLC- β3 increases up to three orders of magnitude the rate of hydrolysis of GTP by its activating G protein. This is a unique mechanism when the PLC-β3 enzyme has the ability to terminate the Gαq protein signal in addition to being activated by it.^{[1] [2]}

Structural highlights

The Gαq subunit consists two domains, one is the GTPase domain and the other is the alpha helical domain. These domains include three regions called switch regions I-III. consisting of N-terminal PH domain, a series of four EF hands, a catalytic TIM barrel and a C2 domain. PLC- β3 engages Gαq throughout three regions. First, an extended loop between the third and fourth EF hands of PLC- β3 directly buttresses switch residues critical for GTP hydrolysis by Gαq. Second, the region of PLC- β3 that connects the catalytic TIM barrel and the C2 domain interacts with both switches 1 and 2 of Gαq. Third, a segment composed of a helix-turn-helix at the C terminus of the C2 domain resides primarily within a shallow declivity on the surface of Gαq formed by switch 2 and α3. Other effectors are known to engage the effector-binding site within Gα subunits. There are a large family of regulator of G protein signaling (RGS) proteins that independently accelerate the GTP hydrolysis in the GTPase domain. PLC-β3 interacts with a surface on Gαq that overlaps almost completely with portions of Gα subunits needed for engagement of RGS proteins and the effector-binding region.

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