3 - Single Pass Receptors - Gray Flashcards
give 4 examples of single pass receptors
and briefly describe their structure
- guanylate cyclase receptors eg atrial naturetic peptide
- TGFB receptor family
- receptor tyrosine kinase family eg insulin, growth factors
- non-catalytic eg cytokine Rs
- single TM helix that has its own enzyme activity or is coupled to another molecule that does. cannot act as own therefore function as dimers
briefly describe guanylate cyclase receptors as a whole
bind ligands and dimerise
intrinsic enzyme activity
converts GTP -> cGMP (2nd messenger) + PPi
Give an example of a guanylate receptor and its role in the body
- eg atrial naturetic peptide receptor has guanylate cyclase activity
- overall aim is to reduce blood volume
- the ANP hormone secreted by heart muscle cells that are stretched (indicative of high blood pressure)
- ANP binds to vascular smooth muscle cells causing them to relax
- also causes kidney to excrete > water and sodium
- overall acts to decrease venous return to the heart therefore decreasing blood pressure
Describe how a guanylate cyclase receptor generates a 2nd messenger. draw a diagram
- binding of ligand eg ANP at extracellular surface causes dimerisation of the receptors
- activates the guanylate cyclase domain which in turn activates the cGMP protein kinase allowing for the conversion of GTP -> cGMP (2nd messenger) and PPi
343 2b
soluble guanylate cyclase is a ___ for other ___
receptor
ligands
which residues do kinases P in eukaryotes?
tyrosine or Ser/Thr residues
what are the role of kinases? name some substrates of kinases
can activate/deactivate other proteins
many kinases that have been P lead to kinase cascade
- substrates= receptors, microtubules, transcription factors, enzymes
describe what enzymes remove P groups and state how these are regulated
phosphatases remove P groups from substrates
they themselves can be Phosphorylated allowing regulation
What TF does TGFB effect? where does this activation take place?
TGFB Phosphorylates smads in the cytosol and allows them to move into the nucleus
What are TGFs? How does TGFB R result in the P transcription factors (draw a diagram of this)
- TGFs small peptides released by proteolysis involved in paracrine / autocrine signalling. normally work to inhibit cell growth and division
- receptor dimerisation (in conjunction with other receptor like proteins) phosphorylates the smad TF
- ser P unmasks a Nuclear localisation sequence and SMAD moves into the nucleus
- altering gene expression to inhibit cell proliferation
343 - 2b word
In more detail, describe what happens when TGFB R binds its ligand. draw a diagram
- its ligand is TGFB
- binding of TGFB by type II receptor promotes dimerisation
- T II recruits and phosphorylates Type I receptor
- TI receptor Ps receptor - regulated SMADs (R-SMADs)
- ## R-SMADs involved in differentiation, proliferation, activation of immune cells (eg T cell activation in INFLAMMATORY response)
What is the result of defects in TGF signalling?
common in cancers
Give an example of a TGFB molecule and explain how it is used in the medical world
bone morphogenic protein
- used in implants to strengthen bones after fracture
- BMPs play role in postnatal bone formation and heart, neural, cartilage formation
give an example of a receptor with no intrinsic enzyme activity
tyrosine kinase linked cytokine receptor
summarise the activity of the enzyme linked single pass receptors. draw a diagram
- receptor itself does not have intrinsic enzyme activity
- tightly couples with a protein kinase (eg tyr kinase)
- ligand binding to receptor dimer causes activation of the cytosolic kinase. causes cross P and activation of the bound kinase
give some examples of cytokines and their functions within the body
INTERFERONS; interfere with viral replication
INTERLEUKINS; T cell activation
ERYTHROPOIETIN; increases production of RBC precursors therefore increasing overall no. RBCs in blood
Describe cytokine R activation. draw a diagram to show this
- binding of L, promotes dimerisation of the receptor (2 monomers are initially close together but Brought further together)
- crossP of the cytosolic JAK kinase domains on activation lip -> conformational change allowing further P of tyr residues on the receptor
Give a summary (with a diagram) of the JAK STAT pathway
- STAT TF binds to the Phosphotyrosine residues on receptor via its SH2 domain. JAK causes P of STAT
- phosphorylated STAT dissociates and dimerises @ SH2 domain
- dimerisation exposes the NLS and STAT moves into the nucleus where it binds to DNA and activates transcription
- phosphatase inactivates JAK and stops the signal
Describe the SH2 domain
- src homology 2 domain
- conserved domain of around 100 aa
- binds to P Tyr residues 1000x more strongly than normal Tyr residues
- over 100 SH2 containing proteins in animals. not found in yeast/plants
What is leptin? give an overall description of functions etc
leptin - “satiety hormone”
- produced by adipose tissue and inhibits hunger. acts on the brain leading to decreased food intake
- similar to interleukins and signal via cytokine receptor and JAK/STAT
Describe briefly how RTK with intrinsic kinase activity stimulate a signal transduction cascade
- ligand binding promotes receptor homo/hetero dimerisation
- cross p of activation lip of cytosolic kinase domains -> activation of tyr kinase activity
- further P of R creating docking points for binding of adapter proteins and initiation of signal transduction cascade
- leading to changes in cell physiology and or gene expression
Describe the class of RTKs and what they bind
- largest family of cell surface receptors
- major class of Rs for peptide hormones eg growth factors, insulin
- many identified through cancer studies (because bind GFs)
Name 2 different ligands for RTKs and state their differences in dimerisation
(draw diagrams)
HUMAN EPIDERMAL GROWTH FACTOR 1;
- binding of this EGF to monomers promote dimerisation through causing a conformational change
- binding of EGF causes 2 loops to further extended and interact with the other loop belonging to a separate monomer therefore promoting their dimerisation -> activation
INSULIN;
- already dimerised receptor is activated through binding of insulin
Give a summary of the human epidermal growth factor receptors
- 4 types of HERs which often act as heterodimers
- HER2 in active loop conformation (doesnt need to bind L) and binds to HER1,3,4
- HER2 gene amplified in 25% breast cancers therefore increasing signalling via ANY HER
name a treatment for breast cancer and state its mode of action. draw a diagram outlining its action
- Herceptin mAb binds to HER2 and prevents its dimerisation therefore blocks downstream signalling and proliferation of cells
- immune cells targeted to tumour cells bring HER2 to the cell
What is the difference between RTKs and cytokine receptors?
- RTKs have a kinase domain as PART of their intracellular cytosolic domain
- cytokine receptors require an additional kinase domain attached to their intracellular domain. it is not a natural part of the protein
Describe (in more detail) the activation of RTKs. draw a diagram
- dimerisation
- protein kinase of each R initially P particular Tyr residues in the cytosolic kinase domains of its R partner.
- transP on the activation lip of the kinase domains results in enhancement of their activation (they are never INACTIVE, but become > active on binding P)
- enhanced kinase activity further P Tyr residues on the receptor
- P Tyr residues of the Receptor act as docking sites for further adapter proteins that facilitate signal transduction
How are RTKs inactivated? Give an example of where see inactivation. draw a diagram
- RTKs undergo endocytosis and are then either degraded or recycled
- endocytosis of the HER1 receptor is increased 10fold on EGF binding and > likely to be degraded
- Rs that are bound and more likely to be degraded and unbound Rs are more likely to be recycled back to cell surface
why is RTK inactivation important?
prevents prolonged cellular signalling
What is the function of an adapter protein? give an example of a complex containing an adapter protein
link activated RTKs to other signalling proteins
eg GRB2 - SOS - inactiveRas GDP
describe how we get activation of downstream signalling from an activated RTK, draw a diagram of the complex that forms
- adapter protein GRB2 containing SH2 and SH3 domains couple the activated R to other signalling proteins
- SH2 domain binds to phosphotyrosine residues
- SH3 domain (60 aa - small protein) binds to proline rich regions of proteins
- eg on the GEF (guanine nucleotide exchange factor) SOS
- brings SOS to the membrane so it can then bind and activate Ras (Ras already present at membrane but SOS binding recruits it to the receptor complex)
Draw a diagram showing Ras cycling between active and inactive forms to regulate a kinase cascade. Explain it as well
- GEF (SOS) helps to activate Ras
- RasGDP = INACTIVE, Ras GTP = ACTIVE
- GEF promotes dissociation of RasGDP and GTP binds
- RasGTP dissociates from its GEF and can then activate a signal transduction pathway. Ras activates a ser thr kinase (eg Raf) which activates a cascade of 3 sequentially activating kinases
- MAPK (once activated) can then move into the nucleus to active tf (eg Myc)
- Ras has inherent GTPase activity (binding of a GAP - GTPase activating protein enhances this activity) and inactivates itself -> RasGDP therefore turning off signal
What is Ras?
- Ras is an oncogene, often found deregulated in cancers
- also a small monomeric G protein found attached to the membrane
some cell types have Ras ____ RTK linked signalling
eg _____
independent
eg EGF R can activate PLC
