Kinetic scaffolding mediated by a phospholipase C-beta and Gq signaling complex

Reciprocal Regulation An essential step in many signaling cascades is inositol lipid hydrolysis catalyzed by phospholipase C–β. The latter is activated by the α subunit of the heterotrimeric G protein Gq, and it in turn inactivates Gαq, thus sharpening the signal. Waldo et al. (p. 974 , published online 21 October) report structural and biochemical data that explain the basis of this reciprocal regulation. One domain of phospholipase C–β binds to activated Gαq. Though the phospholipase C–β active site remains occluded in the structure, the plug is probably removed upon G protein–dependent orientation of the lipase at the membrane. A second domain of phospholipase C–β accelerates guanosine triphosphate hydrolysis by Gαq causing the signaling complex to dissociate.