Question

Which enzyme is directly responsible for activation of GTP binding proteins?

1) Guanine nucleotide exchange factor
2) GTPase activating group
3) Rase
4) Protein kinase
5) Protein phosphatase

Answer 1

The Guanine nucleotide exchange factor (GEF) is the enzyme responsible for activating GTP binding proteins by facilitating the exchange of GDP for GTP on the G-protein. Option number 1 is correct.

Step-by-step explanation:

The enzyme directly responsible for the activation of GTP binding proteins is the Guanine nucleotide exchange factor (GEF). GEFs facilitate the exchange of GDP for GTP on the G-protein, thereby activating it. Once activated, the G-protein can engage with and regulate downstream effector proteins such as adenylyl cyclase, which leads to a cascade of cellular events, including the production of cyclic AMP (cAMP) and activation of a class of enzymes known as protein kinases. These kinases are responsible for phosphorylating various substrate molecules, altering their activity and changing cellular processes.

It is important to differentiate between GEFs and other proteins such as GTPase-activating proteins (GAPs), which accelerate the hydrolysis of GTP to GDP, thus inactivating the G-protein. Mutations affecting these regulatory proteins, like in the case of the RAS G-protein in certain cancers, can lead to uncontrolled cell growth due to continuous activation of the G-protein and its downstream signaling pathways.