14 - Autoinhibition - Williamson Flashcards
does autoinhibition work best for intra/intermolecular bonding? draw a diagram highlighting the differences
INTRAMOLECULAR - local conc is higher and allows for easier binding because closer proximity. these intramolecular binding events come together much more quickly than intermolecular
does autoinhibition work best for intra/intermolecular bonding? draw a diagram highlighting the differences
INTRAMOLECULAR - local conc is higher and allows for easier binding because closer proximity. these intramolecular binding events come together much more quickly than intermolecular
give 6 examples of systems that use autoinhibition to stop the signalling pathway
EGF receptor adaptors - Grb2 Sos Src kinase Abl kinase Raf
how is the EGF R normally inhibited and state what happens during its activation. draw a diagram
- inhibited @ its intracellular side
- binding of L -> dimerisation
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draw a diagram showing how a specific adaptor is autoinhibited
- Grb2 - SH3 domains bind to the pY binding domains of SH2
- weak intramolecular binding competes with stronger intermolecular binding
draw a diagram and explain how Sos acts as a GEF.
- Grb2 binds proline helix of Sos and recruits it to membrane
- once Sos at membrane an additional Ras-GDP binds
- this binding activates the GEF
- RasGTP is even better at activating Sos for further RasGDP activation and replacement for RasGTP
- PH binds PIP2 and increases Sos activity even more
- target RasGDP displaced with GTP
how is Sos activity increased so it better acts as a GEF
- RasGTP bound makes Sos a better GEF for further rounds
- PH binding PIP2 and increasing activity even more
how is src kinase autoinhibited ?
- SH2 domain binds pY near C terminus
- SH2 pY fixes a linker containing proline-rich sequence
- SH3 binds the linker and locks everything shut
- the linker is locked in a way that the AS is distorted
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what signalling pathways are associated with Src kinases? what can happen when we get unwanted activation of these Src kinases?
JAK/STAT systems can be associated with src kinases
- Src kinases are virally encoded oncogenes - unwanted activation -> unwanted signals
how can the autoinhibited src kinase be activated? DAG
- deP of the pY
- binding of SH2 to a better pY sequence eg in substrate
- binding of SH3 to better proline rich sequence
how is Abl kinase autoinhibited?
- SH2 binds to the back of the kinase (not to pY) and is locked in by an N-terminal peptide held in a hydrophobic pocket
- SH3 bound to polypro line sequence in linker
- ## kinase AS is locked in place and cannot close on substate therefore INACTIVE
what happens during the activation of the Abl kinase that enables it to be bound at the membrane
- myristolated N terminus comes loose and inserts into the membrane
what is the consequence of these systems having the same basic mechanisms of activation but Differing in their auto inhibition/the scaffolds present? give an example
drug intervention needs to be more specific for certain kinases. eg may target associated scaffolds, autoinihibited structures eg Gleevec (anticancer drug) binds active site of Abl kinase but NOT Src kinase. this is because of the different ways the AS is locked in
how is Raf autoinhibited? when is it released from this state?
- 2 halves of the hairpin in Raf locked in together. 14-3-3 binding locks this in place
- released upon Ras GTP binding
how have receptor kinase systems evolved? what was the first signalling system and why?
essential basic system has evolved with the addition of extra bits eg scaffolds, adaptors, autoinhibited states
- first system probably smads because they are the simplest
