Receptor Tyrosine Kinases Flashcards
What are the ligand for these Receptor Tyrosine Kinases?
EGF R Insulin R Trk A,B,C PDGF R m-csf FGF R VEGF R
EGF R - EGF
Insulin R - Insulin
Trk A,B,C - NGF, BDNF, NT-3
PDGF R - Platelet derived growth factor
m-csf receptor - Macrophage colony stimulating factor
FGF R - Fibroblast growth factor
VEGF R - Vascular endothelial growth factor
What are the importance of RTKs?
- Function as oncogenes
- Important for wound healing (fgf r)
- Angiogenesis (VEGF)
- neuronal survival (NGF R )
What on earth is RTK? XD
- cell- surface receptor
- TYROSINE KINASE DOMAIN in the cytoplasmic domain have intrinsic enzymatic activity
- mostly receptor for peptide/protein growth factors
- regulate growth and differentiation and survival
- single (ONE) transmembrane domain
- usually single polypeptide- insulin receptor family is an exception
- ## ec binding site has often immunoglobulin or fibronectin domains
What are the four mechanism of ligand-receptor complex and binding?
lemmon 2010
- Ligand mediated dimerization
> TrkA (NGF)
>NGF contact each other - Ligand mediated dimerization with receptor contacts
> KIT ( STEM CELL FACTOR)
> SCF binds with KIT
> KIT contact each other at D4-D5 region - Multiple contact with FGF and Heparin Molecules
> FGFR and FGF ( and heparin molecules)
> Dimerization is caused by a) bivalent ligand binding b) direct receptor-receptor contact c) accessory molecule involved
4) The receptor mediated extreme ( EGFR/ErbB family)
> EGFR family (EGF)
> ligand does not contribute to the dimerisation interface
how do we find out about RTK signalling?
Experiment with the drosophila eye missing R7
- photosensitive neurons in each ommatidium are RETINULA and R cells ( R1-R8)
- RTK sevenless, because it regulates development of R7 ( seven-less… geddit?)
- sevenless mutation in drosophila gives rise to flies with lack of R7
*
Explain experiment for R7 in drosophila
- Trying to test for sevenless ( a type of RTK)
- sevenless mutation in drosophila gives rise to flies with lack of R7
- DOUBLE MUTATION ( no sevenless but active Ras = sev-:RasD) bypass sev, can generate R7 neuron (instead of cone cells)
- R8 express BOSS ( bride of sevenless), ligand for sevenless (RTK)
- this experiment also leads to the discovery of SH2 containing Grb2, sos (GEF) , Ras
- SOS = guanine nucleotide exchange factor, activating Ras by exhanging GDP with GTP
The Insulin Receptor
heterotetramer (2a,2b)
when bind with insulin (ligand), conformational change in the insulin receptor structure is different from what are seen in other RTK
conformation change activates the TKD in the B subunit
B subunit can phosphorylate both a) cytoplasmic domain and b) downstream substrate (IRS - insulin receptor substrate)
Describe the activation mechanism of Tyrosine Kinase Domain
dimerization of the extracellular domain activates the intracellular domain
- Different activation mechanism in each RTK
essentially - TKD contain : C lobe and N lobe and activation loop
- donor and receiver
in KIT
^^ juxtamembrane region ( red line) stabilises inactive state
^^ phosphorylation of tyrosine on the juxtamembrane region allow KIT to relax and be in an active conformation
in INSULIN
$ tyrosine phosphorylation disrupts the auto-inhibition in INSULIN/FGF
$ activation loop block access to C lobe
$when the C lobe is accessible, it can bind to ATP/ protein substrate and in active conformation
TKD autoinhibition by the Activation Loop
- insulin and FGF Receptor
- activation loop occlude the c lobe, blocking access for ATP and protein substrate
- transautophosphorylation disrupt the cis-autoinhibitory interaction ( geddit?)
(unlike EGFR)
Juxtamembrane autoinhibition
eg : KIT - STEM CELL FACTOR
- many RTK and cis-inhibited by element outside TKD ( eh juxtamembrane region)
- Juxtamembrane region stabilizes autoinhibited conformation by making contact with the TKD parts such as the activation loop
- receptor dimerization trans-autophosphorylate the tyrosines on these juxtamembrane region, so it disrupts the cis-inhibition
Autoinhibition by C-terminal sequences
Eg Tie2
- c terminal tail region ( contains tyrosine trans-autophosphorylation sites) blocks the protein substrate access to the active site
- autophosphporylation disrupt this inhibition
Assymetric dimer of c/n lobe
- TKD in one receptor of a dimer is oriented assymetriccally than the other one
- donor and receiver
- donor c lobe phosphorylate receiver N lobe, disrupt the autoinhibition `
Describe the signalling in Receptor Tyrosine Kinase
- Autuphosphorylation - RTK phosphorylate themselves such as on the tyrosine residues in the activation loop in the TKD
- Phosphotyrosine act as assembly site for downstream signalling molecule that have SH2 or PTB domain
- Signalling molecule can also bind to the RTK via a docking protein, such as Gab1
assembly of protein complexes in RTK signalling
- assembly of protein complexes in RTK signalling
1) provide branching points in signalling network
What are the signalling molecules that can bind to phosphotyrosine in the RTK?
- Grb2 - via SH2 domain
- Shc
3, PLC-gamma
and many other (why cant you be more vague)
