Signaltransducing trimeric G proteins consist of three subun

Signal-transducing trimeric G proteins consist of three subunits designated alpha, beta and gamma. As we just discussed, the Ga subunit is a GTPase switch protein that to cycles between a and inactive states depending on whether it is bound GTP or GDP. Review the steps for ligand induced activation of effector proteins mediated by the G proteins. Suppose that you have isolated a mutant Ga that has trimeric would this mutation an increased GTPase activity. What effect have on the G protein and the effector protein?

Solution

so, basically in other words we are talking about G -protein coupled receptors here.

The basic steps in the ligand induced activation of the effector proteins mediated by G proteins are as follows:

1. GPCR are the protein cell surface receptors. The ligand to these receptors are small peptide hormones, neuro transmitters etc. Now, the receptor proteins are assosiated with heterodimer proteins that are G proteins having alpha, beta nd gamma subunits as decribed in the question

2. The ligand binds to the receptor. It activates the G-protein . The activation is by the replacement of the GDP (already attached) by GTP

3. The activated G -protein dissosiates into alpha + (beta-gamma complex)

4. activated G -protein now starts secondary messanger pathways

5. cyclic AMP pathway: alpha subunit of G -protein activates the adenylyl cyclase --> catalyse the fornation of cAMP--->activates protein kinase and other proteins.

6.A different type of G-alpha activates the enzyme phospholipase C.

part II ) Inactivation occurs because G-alpha has intrinsic GTPase activity. so, GTP hydrolyses then inactivates the G-protein. mutatation will lead to inactivated G protein and the effector protein will also not affected by it.