Gαq and the Phospholipase Cß3 X-Y Linker Regulate Adsorption and Activity on Compressed Lipid Monolayers.

ABSTRACT

Phospholipase Cß (PLCß) enzymes are peripheral membrane proteins required for normal cardiovascular function. PLCß hydrolyzes phosphatidylinositol 4,5-bisphosphate, producing second messengers that increase intracellular Ca2+ level and activate protein kinase C. Under basal conditions, PLCß is autoinhibited by its C-terminal domains and by the X-Y linker, which contains a stretch of conserved acidic residues required for interfacial activation. Following stimulation of G protein-coupled receptors, the heterotrimeric G protein subunit Gαq allosterically activates PLCß and helps orient the activated complex at the membrane for efficient lipid hydrolysis. However, the molecular basis for how the PLCß X-Y linker, its C-terminal domains, Gαq, and the membrane coordinately regulate activity is not well understood. Using compressed lipid monolayers and atomic force microscopy, we found that a highly conserved acidic region of the X-Y linker is sufficient to regulate adsorption. Regulation of adsorption and activity by the X-Y linker also occurs independently of the C-terminal domains. We next investigated whether Gαq-dependent activation of PLCß altered interactions with the model membrane. Gαq increased PLCß adsorption in a manner that was independent of the PLCß regulatory elements and targeted adsorption to specific regions of the monolayer in the absence of the C-terminal domains. Thus, the mechanism of Gαq-dependent activation likely includes a spatial component.