|MoBio||G Protein Effectors||Chapter 6|
Effectors are the target molecules of G protein α or βγ subunit. Table 6-D-1 lists the major effectors of the α subunit. The βγ subunits may act on adenylyl cyclase, phospholipase A2, phospholipase C, ion channels, calcium ATPase etc.
Phospholipase C (PLC) also cleaves phospholipids, but at a different site than PLA2, thereby generating diacylglycerol (DAG). There are many types of PLC: β, γ, δ and others. The effector of G protein α and βγ subunits is PLC-β.
Second messengers are the signaling molecules generated by the stimulation of cell-surface receptors. For example, cAMP, arachidonic acid, DAG and IP3 generated by the activation of G-protein-coupled receptors are second messengers. The agonists which activate G-protein-coupled receptors are first messengers.
Table 6-D-1. Mammalian G protein α subunits.
Note: "(+)" means "activate" and "(-)" means "inhibit". Upon binding of the cholera toxin, the Gα-bound GTP cannot be converted into GDP so that the G protein remains in the active state. By contrast, pertussis toxin prevents GDP release from the α subunit so that the G protein is locked in the inactive state.