What role does an activated GPCR play in G protein activation?

What role does an activated GPCR play in G protein activation?

• A. It acts like the GAP for the alpha subunit
• B. It acts like the GEF for the alpha subunit
• C. It acts as the GAP for the monomeric Ras protein
• D. It acts as the GEF for the monomeric Ras protein

Answer: (B)

An activated G protein-coupled receptor (GPCR) plays a crucial role in the activation of G proteins by functioning as a guanine nucleotide exchange factor (GEF) for the alpha subunit of the G protein. When a ligand binds to the GPCR, it undergoes a conformational change that allows the receptor to interact with the G protein associated with the cell membrane. This interaction promotes the exchange of GDP for GTP on the alpha subunit of the G protein, thus activating the G protein. Once GTP binds, the alpha subunit undergoes a conformational change, which enables it to dissociate from the beta and gamma subunits, allowing it to interact with downstream effectors in the signaling pathway. This process of facilitating the exchange of GDP for GTP is a characteristic function of GEFs, which is why the role of an activated GPCR is accurately described as acting as a GEF for the alpha subunit of G proteins. The other roles mentioned in the choices do not align with the function of GPCRs. For instance, while GAPs (GTPase-activating proteins) are responsible for accelerating the hydrolysis of GTP to GDP, GPCRs do not perform this action.

An activated G protein-coupled receptor (GPCR) plays a crucial role in the activation of G proteins by functioning as a guanine nucleotide exchange factor (GEF) for the alpha subunit of the G protein. When a ligand binds to the GPCR, it undergoes a conformational change that allows the receptor to interact with the G protein associated with the cell membrane. This interaction promotes the exchange of GDP for GTP on the alpha subunit of the G protein, thus activating the G protein.

Once GTP binds, the alpha subunit undergoes a conformational change, which enables it to dissociate from the beta and gamma subunits, allowing it to interact with downstream effectors in the signaling pathway. This process of facilitating the exchange of GDP for GTP is a characteristic function of GEFs, which is why the role of an activated GPCR is accurately described as acting as a GEF for the alpha subunit of G proteins.

The other roles mentioned in the choices do not align with the function of GPCRs. For instance, while GAPs (GTPase-activating proteins) are responsible for accelerating the hydrolysis of GTP to GDP, GPCRs do not perform this action.