G-Protein α Subunit Chimeras Reveal Specific Regulatory Domains Encoded in the Primary Sequence
Within the GTPase family of proteins the members referred to as G-proteins provide a signal transduction coupling mechanism for many cell surface receptors as described in other chapters in this volume. G-proteins are responsible for regulating an intracellular effector, such as an ion channel or an enzyme, in response to an activated receptor (Johnson and Dhanasekaran 1989). G-proteins exist as heterotrimers composed of α,β, and γ subunits. The G-protein β subunit is the component that binds GDP and GTP. Receptors coupled to specific G proteins catalyze GDP dissociation, allowing GTP to bind. The GTPα complex in turn regulates the activity of specific effectors. The lifetime of the activated GTPα complex is controlled by an intrinsic GTPase encoded in the α subunit which hydrolyzes the bound GTP to GDP (αGDP) returning the a subunit to an inactive state.
KeywordsAdenylyl Cyclase Cholera Toxin Pertussis Toxin GTPase Activity Adenylyl Cyclase Activation
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