2. G protein-coupled membrane receptor, or metabotropic receptor constitute a large family with more than 500 members o has seven transmembrane ahelices o Prolonged exposure of a cell to a particular agonist often leads to the cells becoming less responsive to that agonist via down-regulation and desensitization of the receptors
2. G protein-coupled membrane receptor, or metabotropic receptor • Prolonged exposure of a cell to a particular agonist often leads to the cell’s becoming less responsive to that agonist via down-regulation and desensitization of the receptors. • has seven transmembrane αhelices • constitute a large family with more than 500 members
3.(heterotrimeric)G protein molecular switch activated (on) state: has high affinity for GTP inactivated (off) state: preferentially binds GDP has three subunits: a, Band y The asubunit is frequently the "business end"of the heterotrimeric G protein
3. (heterotrimeric) G protein • molecular switch activated (on) state: has high affinity for GTP inactivated (off) state: preferentially binds GDP • has three subunits: α, βand γ • The αsubunit is frequently the “business end” of the heterotrimeric G protein