RTKs I Flashcards
3 types of enzyme coupled receptors
RTK, tyrK associated receptors, receptor ser/thr kinases
RTKs
Single span TM protein - extracellular ligand binding domain, intracellular tyrosine kinase domain. Ligand binding results in trans-autophosphorylation of the receptor.
How many genes do humans have encoding RTK
~60
What happens when ligands bind to RTKs
Dimerisation
What favours autophosphorylation
The proximity of kinase domains in the RTK
What are the distinct phases of autophosphorylation
Activation loop then cytoplasmic tail/ RTK-associated proteins
What are SH2 (& PTB) domains used for?
Cellular effectors and adaptors use it to bind to phosphotyrosines
RTKs in cancer
Over-expressed or mutated
How to study RTKS
- Westerm blot of cell lysate; 2. Immunoprecipitation with antibody against phosphotyrosine
How can cellular responses be monitored?
Cell counting, quantifying DNA synthesis (proliferation), direct microscopic observance (migration etc)
What happens when EGF binds?
Exposure of dimerisation arm
Ligand dependent dimersation isn’t the only way RTKs work. Explain.
Some RTKs non-covalently linked, some require higher order clustering for full activation and some require co-receptors. Insulin receptor is a covalent, disulphide linked, dimer.
What is an essential co-receptor for FGFRs?
Heparan sulphate
What allows activation to spread faster?
Receptor clustering
How is the tyr kinase domain of the EGF receptor activated?
Allosteric mechanism
Examples of intracellular signalling proteins that bind to pTyr residues.
- PLC-gamma. Produces 1,2-diacylglycerol and IP3. Leads to PKC activation and Ca2+ release from ER; 2. PI 3-kinase. Phosphorylates lipids, which become docking sites from more effectors; 3. Non-enzymatic adaptors (Grb2, Shc, IRS1..). Lead to activation of small GTPase Ras and downstream signalling (MAP kinase pathway).
What are the phosphotyrosine binding domains?
PTB and SH2
Describe SH2 domains
Recognise phosphotyrosine residues in specific context - recognition sequences vary but all contain hydrophobic residue C-terminal to the phosphotyrosine
How many SH2 domains does the human genome encode
> 100
Describe SH3 domains
Recognise proline-rich sequences (type II poly-Pro helix).
SH3 recognition sequence
Arg-Lys-Leu-Pro-Pro-Arg-Pro
Where are the docking sites for adaptor proteins (e.g. Grb2)?
On the RTK itself or on receptor-associated proteins (IRS1)
