Jan 23 Flashcards
(11 cards)
What does Grb2 interact with using what domains?
It has SH2 for PO4’d Tyr, SH# for poly-proline that SOS has
Are PI lipid derived 2nd messengers for GPCR and/or RTKs?
They exist for both types
How could you see if secondary messengers made from PI experimentally?
Feed the cells radioactive phosphate, then see that it apperas in PI lipid. Then when add acetylcholine, it is suddenly present in molecules free floating in solution (secondary messengers)
How is IP3 generated and what does it do?
- Have PI lipid in only inner leaflet of plasma MB
- PI4 kinase PO4’s carbon 4 using ATP as PO4 source
3.PI4 5-kinase PO4’s carbon 5 to make PIP 4,5. ATP used again
4.Ligand binding causes BY complex of G-protein to activate PLC-B
- PLC-B will hydrolyze PI(4,5) to generate DAG and IP3
- IP3 binds to receptor on ER
- Ca2+ is 10000x higher in ER than cytosol, channel opens so more Ca2+ now in cytosol
Which domains of PLC-B are there, roles?
PH domain binds to PI-4,5
EF hand binds to Ca2+
Catalytic domains will do hydrolysis to release IP3
C2 domain will bind to a phospholipid in MB to help PLC-B dock to MB
What 3 domains bind to PI-3P lipid?
It is phosphoinositine ring with PO4 as part of joining ring to glycerol, but has another PO4 on carbon 3. It binds to PH , PX, and FYVE domains
What are the 4 classes and the subclasses of PI3Ks?
They phosphoryalte the carbon 3 of PI substrates. Class 1 PO4 the PI-4,5, so make PI-3,4,5. Class 1A downstream of of RTks, Class 1B is downstream of GPCRs.
There are 4 class 1 genes in humans, alpha, beta, gamma, and delta
There is also class 2 and 3
How are class 1 PI3Ks activated by growth factor receptors?
Following receptor dimerization and autophosphorylation, Grb2 binds to PO4’d Tyr with SH2 and brings SOS with it using its SH3 domain (poly-proline).
- SOS is a guanine exchange factor (GEF) for Ras that is embedded in MB with lipid. When SOS binds is causes GDP to pop out of Ras, GTP goes in as [GTP] is high in cytosol.
- p85 domain of class 1A PI3ks is binding to PO4’d Tyr too, and this effect plus active Ras activates the p110 domain of it (synergystic activation), then cleaves PIP3 from PI(4,5)
What is synergystic activation?
It is when each activation has an effect, but it is far greater when many things activate it. EX: 2 factors activate this protein, each factor increases its activity 50 times, but both binding is like 250 times or higher
How many isoforms of the 4 of PI3Ks are downstream of GPCR and RTKs?
1 isoform downstream of GPCRs, 3 of RTKs
