CPPS 325 FINAL EXAM Questions and Answers 2023

CPPS 325 FINAL EXAM Questions and Answers 2023 What are the 5 well-known enzyme-linked cell surface receptors? 1. Receptor Guanylyl Cyclase: produces cGMP 2. RTK: phosphorylate tyrosine residues leading to association of signalling molecules and cascade 3. TK Associated Receptors: associate with proteins having TK activity 4. Receptor Tyrosine Phosphates: Removes phosphate on tyrosine residues 5. Receptor Serine/Threonine Kinases: phosphorylate specific Serine/Threonine residues on IC signalling molecules How are RTK and TK Associated Receptors different? RTK phosphorylate tyrosine while associated receptors bind/find proteins with TK activity to initiate the cascade of signalling. What is the reciprocal of RTK? Receptor Tyrosine Phosphatases. They take the phosphate off the tyrosine residues to inactivate signalling cascades. Ex. Transforming GF Beta superfamily of receptors, cell type dependent. What is the major mechanism for receptor signal transduction? Tyrosine kinase phosphorylation RTK vs. Serine/Threonine Phosphorylation ? Tyrosine phosphorylation is rare (1%) relative to serine/threonine residue phosphorylation. Tyrosine phosphorylation is the major mechanism of receptor signal transduction. What is the net effect of activated TKs? Tyrosine phosphorylation on target proteins. What do TK pathways mediate? Cell growth (growth factors), differentiation, host defense, metabolic regulation, cell survival pathways (survival factors). What are amplifiers of the TK pathways? PI3-K - PIP3 PLC - DAG and InsP3&Ca2+ What are RTK mediated actions in the cell? regulation of cell proliferation, differentiation, and cell motility, promotion of cell survival and modulation of cellular metabolism. TKs exist in either the cytosol or as transmembrane receptors, what are the differences in the two types? Cytosol receptors have an src N-terminal region. Cytosol has no membrane spanning domain. TM receptor has a single membrane spanning hydrophobic TM domain. Ex) Epidermal GF RTK. What is src? Src is a non-receptor TK, so it does not span a membrane. It is a tyrosine kinase. And although it is cytoplasmic TK it can still bind to activated RTKs. What is contact inhibition confluency? Stops Src domains signalling and therefore cells stop dividing. If there is an issue then cancer can result and mutation causes an inhibition of the stop signal so the cells keep growing and dividing. What are SH domains? Src homology domains. Src and other proteins that have src-homology domains can bing to activated RTKs. What are the different SH domains in proteins? There are SH1, SH2 and SH3 domains. What isSH1 domain characterized by? Catalytic domain of a protein, for example the receptor. and it has the kinase activity. It is responsible for phosphorylating tyrosine residues. What is SH2 domain characterized by? Binds peptides with consensus (positional information on C-terminal side of the phosphorylated tyrosine). Very specific. Mediates protein-protein interactions in cellular signalling cascades. Very common in proteins outside the src family. What do SH2 and SH3 domains have as a common funciton? They mediate protein-protein interactions in cellular signalling cascades. Very common in proteins outside the src family. What is SH3 domain characterized by? Interacts with proline-rich peptide targets (minimal consensus). Mediate protien-protein interatctions in the cellular signalling cascade. Very common in proteins outside the src family. What are PTB domains? (Phosphotyrosine binding domain) Bind to phosphorylated tyrosine. Functional equivalent of the SH2 domain, except for the positional informational. Is not the C-terminus like SH2, but the N-terminus side of the phosphorylated tyrosine. shc is a PTB protein. What is the normal action that stops signalling for cell division in the src pathway? Contact Inhibition Confluency How do PTB and SH2 domains differ? SH2 domains binds consensus on the C-terminus. PTB domains binds the N-terminus. They both mediate cellular signalling. What is shc? PTB protein that docks at the N-terminus consensus docking site. What activates a RTK? Ligand/agonist binding Upon ligand binding the two activation pathways are? 1. Conformational change 2. Dimerization What happens with conformational change activation? A conformational change that is sufficient enough to activate SH1/catalytic domain results in phosphorylation. What is the only example of conformational change activation? Insulin receptor kinase. All other RTKs are activated through forms of dimerization. What are the two forms of dimerization? i) Receptors exist as unactivated dimers until ligand binds (Twist theory) ii) exist as monomers that are brought together and activated by ligand binding. What is the most common method of dimerization activation? Receptors existing as monomers. What is the Twist Theory? RTKs exist as formed dimers and when a ligand binds the dimer undergoes a twist/shift in shape so the catalytic domains can become fully active and therefore allow for autophosphorylation in key tyrosine residues outside the catalytic domain. What is the monomer dimerization activation pathway? The monomers need to dimerize to fully activate the TK/SH1 domains. Ligand must bind external domains of two monomer RTKs so they dimerize. This results in increased enzymatic activity of the IC catalytic SH1/TK domains by phosphorylating key tyrosine residues outside the catalytic domain. Transphosphorylation of tyrosines occurs so the kinase activation can occur, and transphosphorylation of regions that create the docking site. The phosphorylated tyrosine residues serve as docking sites for cytoplasmic signalling molecules. What does RTK activation require? Dimerization and transphosphorylation!! Where are tyrosines phosphorylated They are first phosphorylated within the kinase/catalytic domains to increase the activity of enzyme and this triggers phosphorylation outside the catalytic/kinase domain that produces a docking site. What does phosphorylation of tyrosines within the kinase/catalytic domain do? Increases the kinase activity of the enzyme. What does phosphorylation of tyrosines outside the kinase/catalytic domain do? It creates high-affinity binding sites for a number of IC signalling properties. What are some IC signalling proteins that bind to the docking sites created by phosphorylation outside the kinase/catalytic domain? - PLC (amplifiers) which leads to release of Ca2+ -SRC TK (non-receptor TK) -Adaptor proteins like Grb-2. (activation of Grb-2 leads to recruitment of SOS and activation of Ras) What is Ras? A small monomeric G-protein anchored to the inner PM involved in many signalling responses when activated to trimeric G-protein. What is Ras regulate by? Ras is regulated by guanine nucleotide exchange factor (GEF) and GTPase activating proteins (GAPs). Ras switches between active and inactive states. Ras G protein inactive bound to GDP. GDP is exchanged for GTP by GEFs and Ras is activated. GAPs accelerate OFF by enhancing the hydrolysis of GTP to GDP. What happens when Ras proteins are mutated? Mutated Ras proteins are unable to dissociate GTP, so they are stuck in the ON or proliferative state. Can lead to cancer. What happens when Ras-GAPs when they are mutated? Mutations lead to disease because the Ras-GAPs proteins can't hydrolyze GTP back to GDP efficiently so Ras stays activated longer than it should. What is SOS? Is a guanine nucleotide exchange factor. How is Ras linked RTKs? An adaptor protein (Grb-2) and a GEF (SOS) link activated RTKs to Ras (downstrea signalling proteins). What is Grb-2? Grb-2 is a adaptor (linker) protein that couples activated RTKs to downstream signalling proteins like Ras. What is Grb-2 composed of ? Composed of SH2 and SH3 domains. What is the function of SH2 domain of Grb-2? SH2 (Src-homology 2) domain of Gr-2 binds to specific phosphotyrosines on activated RTK. Mediates activity. What is the function of SH3 domain of Grb-2? SH3 is involved in protein interaction and binds to proline rich regions of SOS. SOS is a GEF so it regulates Ras activity.