Phosphoinositide Phospholipase C - Isozymes and Activation

Isozymes and Activation

The Phospholipase C family consists of 13 isozymes split between six subfamilies, PLC-δ (1,3 & 4), -β(1-4), -γ(1,2), -ε, -ζ, and the recently discovered -η(1,2) isoform. Depending on the specific subfamily in question, activation can be highly variable. Activation by either G_αq or G_βγ G-protein subunits (making it part of a G protein-coupled receptor signal transduction pathway) or by transmembrane receptors with intrinsic or associated tyrosine kinase activity has been reported. In addition, members of the Ras superfamily of small GTPases (namely the Ras and Rho subfamilies) have also been implicated. It should also be mentioned that all forms of Phospholipase C require calcium for activation, many of them possessing multiple calcium contact sites in the catalytic region. The only isoform that is known to be inactive at basal intracellular calcium levels is the δ subfamily of enzymes suggesting that they function as calcium amplifiers that become activated downstream of other PLC family members.