Berg Tymoczko Stryer Biochemistry Seventh Edition Chapter 14 Signal Transduction Pathways Copyright 2012 by W H Freeman and Company Concepts cid 190 General principals cid 190 e g adrenergic receptor cid 190 e g Angiotensin II receptor cid 190 e g Insulin receptor G couple protein activation PKA signal transduction Desensitization IP3 and DAG activation PKC signal transduction Ca2 as messenger Cross phosphorylation dimer IRS and PIP3K adapters PKB signal transduction cid 190 EGF receptor Cross phosphorylation dimer Ras GTP as phosphorylation trigger cid 190 Diseases and signal pathway defects Principals of signal transduction Cells have evolved highly efficient signal integration and communication systems to rapidly respond an adapt to changes in their environment General principals 1 Signal sensing generally at the plasma membrane 2 Signal integration by conformational changes 3 Generation of second messengers cAMP Ca2 IP3 DAG inside cells 4 Activation of effectors and amplification through cascades 5 Response 6 Signal termination feedback Feedback mechanisms are also at play to control the intensity of response to a stimulus Focus on beta adrenergic receptor signal transduction Fligh and fight response to danger Amplification Focus on beta adrenergic receptor signal transduction 2 AR 7 TM receptor for epinephrine Binding of epinephrine induces conformational in cytoplasmic domains of 2 AR Activation of the receptor Focus on beta adrenergic receptor signal transduction Focus on beta adrenergic receptor signal transduction Inside cells G protein an heterotrimer bound to and subunits and bound to GDP in its unactive form at the plasma membrane G protein G s activated upon conformational change of 2 AR by opening the GDP binding site and exchange with cellular GTP GTP binding conformational change of G s and dissociation of and subunit 1st amplification process 1 AR stimulates many G s Focus on beta adrenergic receptor signal transduction Focus on beta adrenergic receptor signal transduction Activated G protein G s GTP diffuses in the membrane and bind to an effector adenylate cyclase Adenylate cyclase converts ATP to cAMP G s GTP binding induces conformational changes in adenylate cyclase for enhanced catalytic activity and production of cAMP Increased production of cAMP in the cytoplasm 2nd amplification Focus on beta adrenergic receptor signal transduction Focus on beta adrenergic receptor signal transduction cAMP binding induces large conformational changes that release PKA into active monomers Amplification Active PKA binds ATP and phosphorylates other proteins on serine residues Phosphorylation cascade 3ird amplification Focus on beta adrenergic receptor signal transduction Amplification beta adrenergic receptor signal reset and termination Reset of G protein GTPase activity intrinsic to G s clocking system Reset by hydrolysis of GTP into GDP slow reaction sec min Association of G s with subunits unactivated form Reset of receptor itself Dissociation of ligand ligand dependent and Phosphorylation of receptor C terminal tail by kinases activated as part of the PKA triggered cascade e g adrenergic receptor kinase negative feedback arrestin binds to the phosphorylated C terminal tail desensitizes the receptor Focus on angiotensin II receptor signal transduction Angiotensin hormone peptide involved in blood pressure control Angiotensin receptor 7 TM receptor that activates G q G protein G q GTP binds and activate phospholipase C an enzyme that has a lipid PIP2 as a substrate PIP2 cleaved into IP3 soluble and DAG membrane Focus on angiotensin II receptor signal transduction Angiotensin hormone peptide involved in blood pressure control Angiotensin receptor 7 TM receptor that activates G q G protein G q GTP binds and activate phospholipase C an enzyme that has a lipid PIP2 as a substrate PIP2 cleaved into IP3 soluble and DAG membrane Focus on angiotensin II receptor signal transduction Angiotensin hormone peptide involved in blood pressure control PIP2 cleaved into IP3 soluble and DAG membrane IP3 triggers Ca2 efflux from ER IP3 Ca2 channel receptor DAG activate PKC PKC requires Ca2 to bind DAG Phosphorylation cascade Ca2 as an intracellular messenger Why is Ca2 a good intracellular messenger Can be stored in the ER Low cytoplasmic abundance of Ca2 large conc changes in response to stimuli Strong interactions with negatively charged aa residues large conformational changes in proteins e g calmodulin Calmodulin Ca2 binding domains called EF hands x4 Calmodulin undergoes large conformational changes after Ca2 binding Active calmodulin Ca2 induces structural changes to other proteins upon binding e g CaM kinases Cooperativity in Calmodulin x4 Ca2 binding sites provides further kinetic modulation of the signal transduction Focus on insulin receptor signal transduction Insulin is released upon sensing increase in blood sugar and triggers uptake of glucose by cells Insulin receptor homodimer 2 identical subunits one chain extracellular and one chain intracellular and transmembrane per monomer homodimer assembly insulin binding pocket Receptor itself is a kinase catalytic site within subunit Two chains 3 disulfide bonds Focus on insulin receptor signal transduction continued Insulin binding Kinase activity of insulin receptor directed to its own tyrosine residues cross phosphorylation Cross phosphorylation done on an activation loop by one subunit on the other and vice versa Phosphorylation of multiple tyrosine residues induce a swing of the activation loop and significant conformational changes in the receptor Focus on insulin receptor signal transduction continued Additional phosphorylation on the receptor induces the recruitment of adapter proteins called insulin receptor substrates IRS IRS bind the receptor on phosphotyrosine and additionally binds PIP2 lipids with a pleckstrin domain IRS are themselves phosphorylated by the receptor on specific Tyr X X Met sequences x4 Phosphorylated IRS provide a site specific signal amplification at the membrane Domains in IRS adapters 6 Focus on insulin receptor signal transduction continued Tyrosine phosphorylated IRS can now attract phophoinositol 3 kinases PIP3K through binding of PIP3K SH2 domain PIP3K add an extra phosphoryl group to PIP2 to give PIP3 6 6 6 Focus on insulin receptor signal transduction continued PIP3 activates protein kinase PDK1 which triggers a phospho cascade through the phosphorylation of Akt protein kinase B Phosph