G-protein linked receptors activate G proteins by reducing the strength of GDP binding. This results in rapid dissociation of bound GDP, which is then replaced by GTP, which is present in the cytosol in much higher concentrations than GDP. What consequences would result from a mutation in the alpha subunit of the G protein that caused its affinity for GDP to be reduced without significantly changing its affinity for GTP? Compare the effects of this mutation with the effects of cholera toxin.
A mutation in which the alpha subunit that causes a reduced affinity in association with GDP without changing its affinity for GTP would result in signaling through G-protein receptors constitutively active. This means that intracellular signaling of the heterotrimetic G-proteins would be independent of ligand binding to its receptor. This is because the ligand binding to the receptor causes a conformational change in the G-protein linked receptors causing the reduction in the alpha subunit's affinity for the GDP molecule. This allows the alpha subunit to now bind GTP and induce intracellular signaling. This ...
A g-protein linked receptors is examined.