Question

Draw the GEF+GAP cycle and show how GAP-KO/KO and GEF-KO/KO impact signaling.

Answer 1

Guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) are a group of regulatory proteins that control the activity of small G-proteins (like Ras) to regulate the cellular functions. In general, the GEFs initiates a signalling cascade by exchanging the GDP to GTP that is bound to a G-protein by changing the conformation of the G-protein nucleotide-binding site, whereas GAPs terminates the activity of the G-proteins by inducing GTP-hydrolysis. The membrane-bound small G-protein coupled receptors cycles between GDP- and GTP-bound states which are also called 'off' and 'on' states respectively. When the G-proteins get activated by the action of GEFs, then it induces the downstream signalling events. The GTP-GDP cycle is also gets regulated by the GEFs. The exchange of GDP from the inactive GTPases is very slow, and while the GEFs dissociates one GDP molecule then the nucleotide-binding domain gets replaced by one GTP molecule as the concentration of the GTP is 10 times higher than GDP in a cell.