Hydrogen‐Deuterium Exchange Reveals Distinct Activation States of PLCβ2 BY G‐Proteins

Abstract

G‐protein coupled receptors (GPCRs) are an important class of cell surface receptors that transduce extracellular stimuli to intracellular signaling events via G‐proteins. One major effector of G proteins is phospholipase C (PLC), which hydrolyzes Phosphatidylinositol 4,5 bisphosphate (PIP2) into Diacylglycerol (DAG) and Inositol 1,4,5, trisphosphate (IP3). PLCβ2 and PLCβ3 isoforms are directly activated by binding Gαq, Gβγ or both. The mechanism of activation of PLCβ2 by Gβγ is unknown, and the binding site(s) for Gβγ on PLCβ remain controversial.Here we use hydrogen‐deuterium exchange mass spectrometry (HDXMS) to understand the conformational dynamics of PLCβ and to answer open questions in the field concerning the mechanism of activation of PLC by Gβγ and Gαq. For these experiments, several complexes were examined with HDXMS: PLCβ2 alone, PLCβ2+ PIP2/Phosphoethanolamine (PE)/Phosphatidylserine (PS) vesicles, or PLCβ2+ PIP2/PE/PS vesicles plus Gβγ or Gαq‐AlF4. Incubation of PLCβ2 with PIP2/PE/PS vesicles strongly protects regions in the C‐terminus, confirming that this region is involved in membrane binding. In the presence of Gαq‐AlF4, PLCβ2 shows protection from deuterium exchange in the helix‐loop‐helix region of the proximal C‐terminal domain (CTD) and the EF‐hand domain on PLCβ2 that exactly correspond to regions shown to interact with Gαq in the Gαq‐PLCβ3 crystal structure. These data validate that our approach accurately reports bona fide protein‐protein and protein‐lipid interactions. Incubation of Gβγ with PLCβ2 does not reveal any regions of strong protection, but rather causes strong increases in deuterium exchange in the of the CTD of PLCβ2, indicating that the CTD of PLC undergoes a large conformational rearrangement upon Gβγ binding. This increase in deuterium exchange of the CTD of PLC is not seen upon Gαq activation. This indicates that there are distinct conformational states of PLCβ induced by Gαq and Gβγ interactions, suggesting that Gαq and Gβγ use different mechanisms for activation of PLCβ. To determine the mechanism of activation of PLCβ, we used a purified reconstitution system of PLC activity. In vitro reconstitution experiments show that CTD‐deleted PLCβ2 exhibits increased activity in response to Gβγ. Additionally, the distal CTD of PLCβ inhibits CTD‐deleted PLCβ2 activity in both lipid‐dependent and lipid‐independent reconstitution system. Taken together, these results suggest that Gβγ activates PLCβ by breaking an autoinhibitory interaction of the distal CTD with the core enzyme of PLC.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.