Receptor Tyrosine Kinases. Ahu Karademir Andrei Vasiliev. Receptor tyrosine kinases (RTK). Cell-surface receptors with intrinsic enzymatic activity (tyrosine kinase) Cytoplasmic domain has tyrosine kinase activity Mostly receptors for peptide/protein growth factors
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Receptor Tyrosine Kinases Ahu Karademir Andrei Vasiliev
Receptor tyrosine kinases (RTK) • Cell-surface receptors with intrinsic enzymatic activity (tyrosine kinase) • Cytoplasmic domain has tyrosine kinase activity • Mostly receptors for peptide/protein growth factors • Regulate growth and differentiation and cell survival
Receptor tyrosine kinases (RTK) • Single transmembrane domain • Usually single polypeptide • Insulin family is an exception • Extracellular binding site has immunoglobulin or fibronectin domains • Intracellular kinase domain includes tyrosines that can crossphosphorylate
Ligands of receptor tyrosine kinases(RTK) • EGF • Insulin • PDGF • FGF • NGF
Activation of RTKs • Ligand binding promotes conformational change and dimerization of the receptor • Some RTK are dimers (insulin receptor) but ligand binding is necessary for activity
Activation of RTKs • Dimerization activates enzymatic activity of the receptor molecule (tyrosine kinase) • Cross-phosphorylation of the cytosolic domain on the partner
Activation of RTKs • Phosphotyrosine residues interact with proteins that have SH2 and PTB domains • Two mechanisms of interactions with the effector • Activation of enzymes with SH2 domains • Through adapter protein
Response of the insulin receptor kinase (IRK) to ligand binding • Heterotetramer (2a, 2b) • Insulin binding leads to change in structure (different from other RTKs) • Conformation change activates b-subunit TK activity • b subunit phosphorylates Tyr residues on cytoplasmic domains as well as downstream substrates (IRS)
Activation of the insulin-receptor Tyr kinase by autophosphorylation. Target protein in substratebinding site Activation loop blocks substratebinding site Inactive (unphosphorylated) Tyr kinase domain Active (triply phosphorylated) Tyr kinase domain
The regulation of Ras activity, a famous downstream molecule of RTK responsible for cancer development
The enzyme PI-3K, activated by interaction with IRS-1, converts the membrane lipid PIP2 to PIP3, which becomes the point of nucleation for proteins in a second and third branch of insulin signaling.
The recruitment of signaling molecules with PH domains to the plasma membrane during B cell activation One PI3K pathway PH domain: pleckstrin homology domain
JAK-STAT signalling system • In the JAK-STAT signalling system, a soluble protein Tyr kinase (JAK) is activated by association with a receptor, and then phosphorylates the transcription factor STAT, which enters the nucleus and alters the expression of a set of genes.
Tyk2 Jak1 Tyk2 Jak1 Jak-STAT Signaling Pathway Activated by -interferon -interferon SH2 domain STAT1 STAT2 STATs dissociate from receptor and dimerize via SH2 domain Nucleus Gene regulatory proteins Transcription www.motifolio.com
Summary • The insulin receptor is the prototype of receptor enzymes with Tyr kinase activity. • When insulin binds to its receptor, each monomer of the receptor phosphorylates the chain of its partner, activating the receptor’s Tyr kinase activity. • The kinase catalyzes the phosphorylation of Tyr residues on other proteins such as IRS-1.
Summary • P –Tyr residues in IRS-1 serve as binding sites for proteins with SH2 domains. • Some of these proteins, such as Grb2, have two or more protein-binding domains and can serve as adaptors that bring two proteins into proximity.