General Flashcards
What is the difference between receptor tyrosine kinase and tyrosine linked kinases?
RTKS have a built-in kinase and tyrosine linked have a separate kinase molecule that they’re linked to.
What are adaptor proteins? What are the interaction domains?
Proteins that connect the intracellular part of the protein to the downstream signalling - used to extend the signalling power of the receptor. Interaction domains are a piece of the protein structure which is found in many types of proteins
How is an allergy developed?
- Sensitization to allergens e.g. in the airways leads to the production of allergen-specific IgE and up-regulation of Th2 cells- leads to B cells making specific IgE and mast cells presenting it for immunity purposes
- IgE-receptor crosslinking leads to the early phase of allergen-induced airway inflammation - next exposure, mast cells causes an increase of histamine and prostaglandins. Cytokines released by immune cells positively feedback on each other to further response. 3.3. Late phase reactions - recruitment of more immune cells causes an increase of inflammation and tissue damage. 4. Chronic stage of allergen-induced airway inflammation. Excess damage alters tissue structure- heavy involvement from Il-4 and IL-3
What are treatments of allergies?
- Stay away from allergen
2. Drugs e.g. beta2-adreno agonists, corticosteroids, anti-histamines, antileukotrines. Anti IgE drugs
What are some new potential treatments for asthma?
Il-4/13 - Therapeutics would either disrupt the receptor or block the cytokines themselves so they can’t activate the receptor. Some can target just one of both. E.f. dupilumab is a monoclonal antibody which targets IL-4 It has been experimentally used to treat severe asthma that can’t be controlled by steroids. Investigations on this done through using mouse models that had been sensitised to antigens
What is special about IgE and its receptor?
IgE is the antibody that is responsible for allergic response. It has a bent structure which causes asymmetric binding, giving it increased selectivity and affinity. The alpha subunit of the receptor on the mast cell has 2 binding sites that are complementary to the IgE bent shape. This creates a 1:1 stoichiometry and a very slow dissociation rate. This makes them stay on the mast cell so it is armed when another allergen comes out. This is what makes the allergic response so quick. Th Fc region on IgE can exist as a tetramer ( a, b 2xg) or a trimer ( a, 2xg). The tetrameric version is the one found on mast cells and basophils. The subunits are linked by disulphide bonds.
What is the disadvantage in using immunotherapy for allergic responses?
Injecting anti-IgE antibodies will only impact new free IgEa. It will not impact ones already on the mast cells because their affinity is so strong. This means treatments may take a while to work because you have to wait for the other ones to die.
Explain the structure and role of FceRa
It is a member of the immunoglobulin receptor superfamily. It has 2 non-identicial immunoglobulin-related domains which form the binding sites for IgE. Its synthesis is regulated by IL-4 (produced by TH2 cells), so involved in the immune response. The b and g subunits are essential for initiating the signal as they contain ITAMS which transduce the signal. The allergens are polyvalent so they span across and link 2 IgEs together (1 IgE per receptor then when they are bound to the receptor the antigen links the 2 antibodies together and brings close the receptors so they signal together). When brought together the ITAMS are targetted for phsophorylation by Src tyrosine kinases. This makes them an SH2 domain.
What effect does intracellular calcium increase have on immune response?
Rapid- degranulation and secretion of histamine and proteases, secretion of TNFa, synthesis and release of leukotrienes and prostaglandins. All of these cause primary inflammation response that fist occurs. Slow - synthesis of more cytokines and chemokines which leads to granulocyte recruitment
How does the increase in intracellular calcium occur?
PLC gamma isoform is activated which causes breakdown into PIP2 to produce IP3 and DAG. IP3 then binds to a receptor in the ER, causing the release of its calcium store. However, the increase in IC calcium from the store is not sufficient to support the signalling needed for an inflammatory response (we know this because if you take away extracellular calcium so the only calcium available is from the ER, you don’t see degranulation). So, the release of calcium from the ER triggers another channel that allows transport of calcium into the cells (for ages people didn’t know what it was but its now known to be CRAC)
What are the 2 major classes of kinases?
Protein kinases (tyrosine kinases and seriene/threonine kinases).
Lipid kinases
Tyrosine, serine, and threonine can be phosphorylated because they have an extra hydroxyl group to which a phosphate group can be added
Explain how apoptosis is mediated by tumour necrosis factors
TNF-a tends to exist as a trimer (not sure whetehr they trimerise on contact with a ligand or if they are held together in a trimer by a PLAD and undergoes a conformational change when a ligand binds. After activation, the cytosolic domains come together and leads to a caspase cascade. the DED on the FasR interacts with the DED on the initiator caspase (procaspase 8). This is catalysed by FADD. The DED is cleaved off and caspase 8 now cleaves off other effector caspases e.g. procaspase 3. Initiator caspases are 8, 9 and 10. The alpha and beta subunits from the initiator and effector caspases join together to form an active caspase. A build-up of cleaved caspases leads to apoptosis. Each caspase has a specific set of substrates therefore they all effect different things and therefore integrate the death signal quickly. Western blots can be used to show the order by which caspases are cleaved
Explain how the intrinsic pathway of apoptosis can be triggered with the help of the mitochondrion
Caspase 8 cleaves bid which leads to truncated tBid. tBid binds to bad and bax and together they bind to the outer membrane of the mitochondrion. This causes the mitochondria to lead cytochrome C. This interacts with Apaf1 and creates an apoptosome. procaspase 9 binds to the apoptosome (becomes its little hat). This starts the caspase cascade and leads to apoptosis.
What is the structure of JAK receptors and how do they signal?
JAK receptors are monomeric and then dimerise on activation by ligand- or they are already dimerised then undergo a conformational change to reveal binding sites for STAT upon activation by extracellular ligand. JAK molecules are not part of the receptor but are closely associated. All of the complexes are phosphorylated. STATs bind together via each other’s SH2 domains. They move into the nucleus and cause transcription of genes
What are the functions of the JAK/STAT pathways
They play a role in immunity - allow differentiation of CD4+ cells into various T helper cell subtypes - activated by different combinations of STATs and ligands. They’re involved in inflammation and haemopoesis. Jak3 mutants and severe combined immunodeficiency.
