Receptor Tyrosine Kinases

Question 1

RTK’s

Answer 1

• extracellular ligand binding domain
• cytoplasmic domain with intrinsic tyrosine activity
• single transmembrane Ahelix
• dimerization from ligand binding
• adaptor proteins required
• Ras: monomeric G protein acts as a GTPase switch protein to further signal downstream kinases

Question 2

Activation of RTK’s

Answer 2

• ligand binds, causes dimerization of receptor
• dimerization allows for trans-autophosphorylation of the cytosolic domain
• leads to phos of additional tyrosine residues
• phosphorylation acts as a docking site for downstream adaptor proteins containing SH2 domains

Question 3

C-src vs V-src

Answer 3

• src= tyrosine kinase
• c-src is normal version. Contains a C-term domain that has inhibitory phosphorylation, inhibits and turns on receptor. Turns off kinase
• v-src: viral, constitutively expressed. Lacks C-term domain, no inhibitory phosphorylation. Can’t turn off kinase.

Question 4

Ras

Answer 4

• monomeric G protein, lipid-anchored. GTPase
• downstream effector of RTK signalling
• very little intrinsic GAP activity
• regulated by GEF and GAP
• in some cancer, Ras binds GTP but no hydrolysis. Mutation prevents GAP binding. RasD. Constitutive expression

Question 5

Ras Activation by FGF

Answer 5

1. FGF binds receptor. Dimerization = kinase activity. Phosphorylation of cytosolic tyrosine receptors
2. GRB2: SH2 binds phos tyrosine’s and SH3 binds proline’s in Sos.
   Sos bound to Ras= inactive but primed
3. Sos promotes GDP dissociation from Ras.
4. GTP binds, active Ras dissociates from Sos
5. Ras-GTP triggers downstream kinase cascade

Question 6

GRB2

Answer 6

• adaptor protein with no kinase activity
• SH2 domain binds cytosolic phos tyrosine’s
• SH3 domain binds tyrosines in Sos

Question 7

Sos

Answer 7

• Essentially a GEF. Removes GDP

Question 8

Ras/MAP kinase pathway

Answer 8

1. Active Ras recruits, binds, and activates Raf
2. GTP hydrolysis in Ras, leads to dissociation from Raf
3. Raf activates MEK
4. MEK activates MAPK
5. Active MAPK translocates to nucleus, activates many TF’s

Question 9

Raf

Answer 9

• inactive when not bound to Ras. Inhibitory protein 1433 bound to N-term regulatory domain
• Active: Raf binds to Ras. inhibitory 1433 dissociates

Question 10

Protooncogenes

Answer 10

• RTK, Ras, Raf, MEK, MAPK, GRB2

Question 11

Tumour-suppressor

Answer 11

• NF-1: GAP cant hydrolyse GTP= Ras constiutively active

Question 12

Protooncogene receptor proteins

Answer 12

• promote proliferation in absence of ligand
• HER2 receptor: muation causes dimerization and activation in absence of ligand
• EGF receptor: deletion causes loss of extracellular ligan binding domain. Leads to consitutive activation of cytosolic kinase domain