Final answer:
The statement about trimeric G-proteins being inactivated by phosphorylation and binding of arrestin and clathrins is false. G-proteins are inactivated by hydrolysis of GTP to GDP, and GRKs initiate receptor desensitization by phosphorylating the GPCR, not the G-protein.
Step-by-step explanation:
The statement that trimeric G-proteins are inactivated when phosphorylated by GRK (G-protein-coupled receptor kinases), which triggers arrestin and clathrins to bind, is false.
The activation and inactivation of trimeric G-proteins involve the exchange of GDP for GTP on the α subunit and the subsequent hydrolysis of GTP to GDP, not phosphorylation.
Activation involves a G-protein-coupled receptor (GPCR) interacting with a trimeric G-protein, causing GDP to be replaced by GTP. Once GTP is bound, the α subunit separates from the βγ dimer and either can trigger specific cellular responses.
The inactivation occurs when GTP on the α subunit is hydrolyzed back to GDP, allowing the α subunit to reassociate with the βγ dimer, thus stopping the signal.
In contrast, GRKs phosphorylate activated GPCRs, which promote the binding of arrestin to the receptor, leading to receptor desensitization and internalization through clathrin-mediated endocytosis. This process does not directly inactivate the G-protein but rather turns off the receptor's ability to activate further G-proteins.