Shemanko lecture 9

Question 1

What are receptor tyrosine kinases (RTKs)?

Answer 1

They are receptors that are activated by extracellular signals
Have ligand binding domains

Question 2

What are cytoplasmic protein-tyrosine kinases?

Answer 2

Are receptors that regulate indirectly by ligand and doesn’t have the signal bind directly

Question 3

What are the types of receptor activations for RTKs?

Answer 3

ligand mediated activation
receptor-mediated activation

Question 4

What happens during receptor mediated activation of RTKs?

Answer 4

two different ligand bind to the receptor, the receptors are brought together and dimerize, kinase domains auto phosphorylate eachother and and other areas of the receptor so cytoplasmic signalling molecules can bind

Question 5

What happens during ligand mediated activation of RTKs?

Answer 5

one ligand binds, the receptors dimerize, change confirmation, and the kinase domains autophosphorylate the receptor and other docking domains so cell signalling molecules can bind

Question 6

The egf receptor (type of RTK receptor) has what kind of domain outside the cell? Inside the cell?

Answer 6

Outside the cell has cysteine rich domains, inside the cell has a tyrosine kinase domain.

Question 7

The insulin receptor (type of RTK receptor) has what kind of domain outside the cell? Inside the cell?

Answer 7

Inside tyrosine kinase
outside has disulfide bonds that keep alpha and beta subunits close

Question 8

The PDGF receptor (type of RTK receptor) has what kind of domain outside the cell? Inside the cell?

Answer 8

inside tyrosine kinase
outside has Immuno globulin domains

Question 9

What types of phosphorylation do RTKs go through?

Answer 9

They autophosphorylation eachother, they phosphorylate the receptor chains, and they have phosphorylation of proteins that come to the receptor

Question 10

What does an SH2 domain do?

Answer 10

Binds phosphorylated tyrosines

Question 11

What does an SH3 domain do?

Answer 11

Binds proline amino acid residues

Question 12

What does a PTB domain do?

Answer 12

Binds phospho-tyrosines

Question 13

What are the four types of signalling proteins that come to the receptor?

Answer 13

Adaptor proteins- Grb2
Docking proteins- IRS
Transcription factors- STATS
Signalling enzymes- PLC

Question 14

What are the three accessory proteins that modulate the activity of small G-proteins?

Answer 14

guanine nucleotide exchange factors (GEFs)
GTPase-activating proteins (GAPs)
Guanine nucleotide-dissociation inhibitors (GDIs)

Question 15

What are GEFs?

Answer 15

they swap out the bound GDP and promote GTP binding and activation of the G protein

Question 16

What are GAPs?

Answer 16

They stimulate hydrolysis of the bound GTP by the G-protein, thus decreases the duration of activity and inactivate the G protein

Question 17

What are GDIs?

Answer 17

they maintain inactive G protein by stopping the GDP from releasing.

Question 18

What is Ras? What is Sos?

Answer 18

Ras is a small monomeric G-protein, Sos helps activate Ras by acting as a GEF for it

Question 19

How do accessory proteins play a role in the activity of Ras?

Answer 19

GAPs shorten the active time of G protein RAS, GEFs activate RAS by exchanging GDP to GTO, GDIs deactivate RAS by stopping release of GDP

Question 20

What do docking proteins like the IRS do?

Answer 20

They provide additional phosphorylation sites by containing a PTB or SH2 that binds to the receptor and phosphorylates creating more phosphorylation sites

Question 21

What is Shp2? What PI3k?

Answer 21

Shp2- is a tyrosine phosphatase
PI3K- is a lipid kinase that phosphorylates inositol rings

Question 22

STATs must be what to be activated and translocate to the nucleus? How do you deactivate the TF STATs?

Answer 22

STATs must be tyrosine phosphorylated by the receptors kinase domain to be activated .
The signal is shut off by proteins blocking the SH2 domain which stops stats from interacting with that domain.

Question 23

Signalling enzymes (proteins) will dock to the receptor if they have what? What happens after they dock?

Answer 23

SH2 domains, after docking they are activated

Question 24

What are the steps of a general MAP kinase cascade?

Answer 24

1. The receptor is activated by a growth factor
2. the receptors kinase domains autophosphorylate and create docking sites
3. The SH2 domain on the signalling proteins recruits Grb and Sos
4. Sos activates the Ras protein
5. Ras protein exchanges GDP to GTP
6. RAS recruits protein kinase Raf, which brings MAP kinase cascade- gets phosphorylated all the way down.
7. MAPK activates the transcription factor by phosphorylation, the TF (Fos and Jun) then activates genes in nucleus such as cyclin D1 and MKP-1
8. MKP-1 ( a phosphatase) inactivates the original map kinase through dephosphorylation. Turns off pathway

Question 25

What is convergence? Give example?

Answer 25

Signals from unrelated receptors lead to activation of a common effector, for example on effector PLC

Question 26

What is Divergence? Give an example?

Answer 26

A signal reaches a variety of effectors, for example: in receptor tyrosine kinases three diff effectors can occur

Question 27

How does a cell pick a pathway in divergence?

Answer 27

Depends on if the docking sites are on or off, the sites aren’t on and off at the same time

Question 28

What can convergence of signals result in?

Answer 28

It can result in a similar set of growth promoting genes to be produced in different target cells for example diff receptors can bind to diff ligands but they can all lead to a docking site of Gbr2.

Question 29

What is Cross-talk?

Answer 29

is when diff signalling pathways block signals from other pathways, for example: camp activated PKA blocks signals from Ras to Raf stopping MAPk pathway