23 Transducing proteins
Many membrane receptors employ intermediary proteins to transduce the events of receptor activation to effector molecules in the cell (e.g. insulin receptor substrate-1 (Ch. 22) and GTP-binding regulatory proteins (G-proteins)).
Heteromeric GTP-binding regulatory proteins (G-proteins)
The heteromeric G-proteins are a large family of proteins that transduce the signal from receptors with seven transmembrane domains (7TMD; G-protein-coupled receptors) to a variety of effector molecules. Each G-protein has a common heterotrimeric structure of three distinct subunits: alpha (α), bound to GDP, beta (β) and gamma (γ). Receptor activation induces a conformational change in the G-protein. This change in structure causes the release of GDP and the binding of GTP in its place. The α-subunit carrying GTP (α-GTP) and the complex of βγ-subunits both dissociate from the receptor and go on to interact with, and activate or inhibit, specific effector molecules (Fig. 3.23.1
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