After ligand binding to a G protein-coupled receptor, what immediate event occurs to the G protein?

After ligand binding to a G protein-coupled receptor, what immediate event occurs to the G protein?

• A. The G protein trimer releases GDP and binds GTP.
• B. The G alpha subunit binds ATP.
• C. The receptor is internalized.
• D. The beta-arrestin is recruited.

Answer: (A)

When a ligand binds a GPCR, the receptor acts as a guanine nucleotide exchange factor for the G protein. The Gα subunit, which carries GDP in the inactive trimer, releases GDP and binds GTP. This GDP–to–GTP exchange activates Gα and causes it to dissociate from the βγ dimer, allowing both parts to regulate downstream effectors. Gα does not bind ATP, which is why that choice isn’t correct. Receptor internalization and beta-arrestin recruitment are related to desensitization and trafficking that occur after signaling, not the immediate G protein activation.

When a ligand binds a GPCR, the receptor acts as a guanine nucleotide exchange factor for the G protein. The Gα subunit, which carries GDP in the inactive trimer, releases GDP and binds GTP. This GDP–to–GTP exchange activates Gα and causes it to dissociate from the βγ dimer, allowing both parts to regulate downstream effectors. Gα does not bind ATP, which is why that choice isn’t correct. Receptor internalization and beta-arrestin recruitment are related to desensitization and trafficking that occur after signaling, not the immediate G protein activation.