Matise - Cell signaling Flashcards
tetradoxin
A toxin usually found in pufferfish that is responsible for disrupting the sodium channel and can kill you.
Nuclear Steroid Hormone receptors
steroid hormones, derived from cholesterol, control gene expression. These steroid hormones are NP and thus can transverse the membrane and bind intracellularly or in the nucleus.
Nuclear Steroid Hormone receptors - estrogen
The estrogen receptor is usually bound to a chaperone protein. When estrogen binds to the receptor, it is released from the chaperone and shows a nuclear import signal. This causes homodimerization and entry into the cell. Dimerized receptors bind to an estrogen response element and, which activates transcription. In breast cancer, we use drugs like tamoxifen in order to act as a competitive inhibitor in order to slow down this process (tam is metabolized into H-tam).
Protein Kinase Receptor
1) extra cellular domain 2) trans-membrane domain 3) cytoplasmic domain that can kinase activity
There are tyrosine kinases and serine/threonine kinases.
Active receptors usually require dimers to come together.
1) ligand binds to receptor 2) subunits dimerize 3) kinases phosphorylate and activate each other 4) additional cytosolic proteins bind phosphorylated receptors
- phosphorylation of a polar R group may turn a relatively NP portion of a protein into a hydrophilic one, which will induce a conformational change which can facilitate interaction with other proteins/molecules.
Protein Kinase Receptor - Ras activation
Basically what happens is that a ligand binds to the receptor, dimerizes the recptors, and the intracellular parts begin to phosphorylate each other. Ras is a G-protein.
1) Grb (G-protein receptor binding) binds to the phosphorylated receptor. It contains SH2 domain, which recognizes phosphorylated Tyrosine.
2) SOS (son of sevenless) binds to Grb and activates Ras. SOS is a Ras GEF (guanine nucleotide exchange factor) that catalyzes the exchange of GDP (inactive) for GTP (active)
3) GAPS (GTPase Activating Proteins) then do the opposite of SOS in that it inactivates Ras by converting GTP to GDP via hydrolysis. In theory this reaction would occur by itself without GAPS but this enzyme speeds up the process.
ras, rab, ran, rac
Ras - receptor signaling and cell division
Rab - traffic of membrane vesicles
Ran - Nucleus/cytoplasm traffic
Rac - actin Cytoskeleton
Nuclear Steroid Hormone receptors - Ras pathway
Ras-GTP is involved in a signaling cascade in which various MAPKs are phosphorylated until eventually it reaches the nucleus which leads to increase in gene expression in proteins involved in cell division.
Ion channels
allows for the flow of ions down their concentration gradient. Obviously involved in signal transduction within neurons. Can be mechanosensory, thermal, voltage gated, ligand gated etc. Mutations can be “loss of function” or “gain of function.” An example of a mutation is cystic fibrosis in which there is a loss of function mutation in the CFTR gene which causes excessive chlorine in the sweat and issues with mucous buildup. The ligand for the CFTR protein is ATP.
How does Ras play a role in cancer?
Oncogenes turn the Ras protein “on” at all times by not allowing it to hydrolyze GTP –> GDP. Most are a mutation in the oncogenes from a Glycine to Glutamine.
Neurofibromatosis Type I
Noonan Syndrome
Neuro - Mutation in the NF1 gene, which encodes neurofibromin-1, a Ras GAP. Because of this, GTP can’t be hydrolyzed to GDP and Ras is overactive.
Noonan - Mutation in PTPN11 gene, which encodes SHP2. Results in a gain of function mutation that causes Ras to be overactive.
7-alpha-helix-receptors
7 transmembrane alpha helices
Coupled to large trimeric G-proteins. One of the subunits, called alpha, contains a Ras-like domain
1) Ligand binding causes the exchange of GTP for GDP. This activates the G-protein, activating a signaling cascade.
2) The alpha, beta, and gamma subunits then dissociate from the receptor and regulate activity of downstream products
- the alpha (Galpha) subunit is responsible for regulating 3 main subclasses of downstream G-products:
a) Gs-alpha
b) Gi-alpha
c) Gq-alpha
Gs-alpha
Gi-alpha
Gq-alpha
Gs - activates adenylate cyclase which activates PKA
Gi - inhibits adenylate cyclase which inhibits PKA
Gq - activates PhosphoLipase Cbeta (PLC), which activates PKC
Desensitization of smell
Beta adrenergic receptor, which is a 7-alpha-helix-receptor will bind epinephrine or norepinephrine. Once one of these is bound, the receptor will be phosphorylated by Beta Adrenergic Receptor Kinase (BARK). The receptor is then bound by Beta-arrestin, which inhibits the interaction with Gs even in the presence of ligand.
Gs/Gi pathway
If NE binds to the receptor, the three subunits dissociate from the receptor, Gs will act to activate Adenylate Cyclase. Once this happens, Adenylate Cyclase will aid in the conversion of ATP–>cAMP, which will then activate PKA, which will cause an influx of calcium into the cell.
If acetylcholine binds instead, Adenylate Cyclase is inhibited and the opposite happens. Intracellular Ca2+ will go down.
Gq pathway
If GTP is bound to Gq, then it will phosphorylate phosphilipase C (PLC), which will then hydrolyze PiP2 into IP3 + DAG.
- IP3 triggers the release of Ca2+ from the SER to the cytoplasm.
- DAG and Ca2+ activate PKC, which lets even more Ca2+ into the cell
PKC is normally inactive because there is a N terminal pseudo-substrate peptide in it’s active site. It is held in place by its C1 and C2 domains.
C1 will bind DAG
In the presence of Ca2+, C2 will bind to phosphatidyl serine (PS)
These two things will remove the substrate from the active site, leaving PKC active.
