Editors' ChoiceG Protein Signaling

Overcoming autoinhibition

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Science Signaling  19 May 2020:
Vol. 13, Issue 632, eabc8254
DOI: 10.1126/scisignal.abc8254

Conformational changes in the C-terminal region of PLC-β2 caused by G proteins release autoinhibition.

When activated by receptors, members of the phospholipase C (PLC) family of enzymes hydrolyze the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate to generate the signaling molecules inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). The PLC-β2 and PLC-β3 isoforms are stimulated by Gαq subunits and Gβγ dimers (from Gi proteins) downstream of G protein–coupled receptor (GPCR) activation. The C-terminal region of PLC-β isoforms contains both proximal and distal C-terminal domains (CTDs), which are connected by a flexible linker region. Fisher et al. used hydrogen-deuterium exchange mass spectrometry (HDX-MS) to investigate the conformational dynamics of PLC-β2 in the presence and absence of membranes, activated Gαq, and Gβγ. HDX rate differences between PLC-liposome complexes and PLC-Gαq–liposome complexes revealed conformational changes that were mostly consistent with the known Gαq-binding regions of PLC-β previously determined by x-ray crystallography. In contrast, the addition of Gβγ to PLC-membrane complexes caused substantial conformational changes along the distal CTD, which were associated with a three- to fourfold increase in PLC-β2 enzyme activity. Comparison of wild-type PLC-β2 with a variant lacking the distal CTD suggested that this domain was autoinhibitory. When expressed in cells, a PLC-β2 variant lacking the linker region between both CTDs exhibited increased basal activity, which was not enhanced by the presence of either Gαq or Gβγ, suggesting that the orientation of the CTDs is important for G protein–dependent PLC-β2 activation. Although the Gβγ-binding surface of PLC-β2 has not been determined and although Gαq and Gβγ interact differently with PLC-β2, these findings suggest that both cause conformational changes in the CTDs that converge to release autoinhibition of the enzyme.

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