CHEM 3050 Lecture Notes - Lecture 55: Phospholipase C, Arrestin, Gtpase
3 May 2018
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CHEM 3050
Lecture 55
Switching Off
- G-proteins have intrinsic GTPase activity
o Hydrolyzes GTP to GDP converted to
Inactive form
- Other enzymes may degrade the 2nd messengers
- Effect of kinase cascades can be reversed by
phosphatases
- Ligand dissociates from receptor
- GPCR may be desensitized by phosphorlylation and
subsequent binding of arrestin which prevents
interaction with G-protein
Another Second Messenger
- Epinephrine also binds with alpha-adrenergic
receptor (another GPCR)
- Receptor binds with the ligand and interacts with
another g-protein
- G-protein activates phospholipases C
o Cleaves PIP2, and forms IP3 + DAG
▪ IP3 is very polar diffuses in cytoplasm
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Document Summary
G-proteins have intrinsic gtpase activity: hydrolyzes gtp to gdp converted to. Other enzymes may degrade the 2nd messengers. Effect of kinase cascades can be reversed by phosphatases. Gpcr may be desensitized by phosphorlylation and subsequent binding of arrestin which prevents interaction with g-protein. Epinephrine also binds with alpha-adrenergic receptor (another gpcr) Receptor binds with the ligand and interacts with another g-protein. G-protein activates phospholipases c: cleaves pip2, and forms ip3 + dag, ip3 is very polar diffuses in cytoplasm, dag is very nonpolar diffuses in membrane, we now have the 2 second messengers. Ip3 triggers opening of ca ion channels which initiates kinase cascade. Dag diffuses in membrane to bind the protein kinase c: this docks pkc at the membrane and activates it, another kinase cascade starts, pkc also requires ca ion for full activation. Effect of ca ion mediated by binding to calmodulin (wraps around target protein)
