Signal Transduction - Medicinal Chemistry PDF

An Introduction to Medicinal Chemistry Chapter 5 DRUG TARGETS SIGNAL TRANSDUCTION Salih Al-Jabour,Dr.rar.nat Pharmacy Department AlQuds University Jerusalem, Palesinte 1. Signal Transduction involving Gs-Proteins...

An Introduction to Medicinal Chemistry Chapter 5 DRUG TARGETS SIGNAL TRANSDUCTION Salih Al-Jabour,Dr.rar.nat Pharmacy Department AlQuds University Jerusalem, Palesinte 1. Signal Transduction involving Gs-Proteins GS-Protein -membrane-bound protein of 3 subunits (α, β, γ) -αs subunit has binding site for GDP -GDP bound non-covalently β γ α GDP 1. Signal Transduction involving Gs-Proteins 1.1 Interaction of receptor with Gs-protein Ligand Cell membrane Ligand G-protein binding binds Recepto r γ ß Induced γ ß Induced γ ß fit fit for α α α G-protein G Protein GDP GTP G-protein alters shape Binding site for G-protein opens GDP binding site distorted GDP binding weakened GDP departs 1. Signal Transduction involving Gs-Proteins 1.1 Interaction of receptor with Gs-protein γ ß γ ß GTP binds Fragmentation α α and release γ ß α Induced fit Binding site recognises GTP G-Protein alters shape Complex destablised Notes: Process repeated for as long as ligand bound to receptor Signal amplification - several G-proteins activated by one ligand αs Subunit carries message to next stage 1. Signal Transduction involving Gs-Proteins 1.2 Interaction of αs with adenylate cyclase Notes: Several 100 ATP molecules converted before αs-GTP deactivated Represents another signal amplification Cyclic AMP becomes next messenger (secondary messenger) Cyclic AMP enters cell cytoplasm with message 1. Signal Transduction involving Gs-Proteins 1.3 Interaction of cyclic AMP with protein kinase A (PKA) Notes: Protein kinase A is a serine-threonine kinase Activated by cyclic AMP Catalyses phosphorylation of serine and threonine residues on protein substrates Phosphate unit provided by ATP 1. Signal Transduction involving Gs-Proteins 1.3 Interaction of cyclic AMP with protein kinase A (PKA) Adenyla te cyclase AT cyclic P AMP Activation Protein Kinase A P Enzyme Enzym (inactive e ) (active) Enzyme-catalysed reaction 1. Signal Transduction involving Gs-Proteins 1.3 Interaction of cyclic AMP with protein kinase A (PKA) Protein kinase A - 4 protein subunits - 2 regulatory subunits (R) and 2 catalytic subunits (C) cAMP C Catalytic subunit C R R R R cAMP C binding sites C Catalytic subunit Note: Cyclic AMP binds to PKA Induced fit destabilises complex Catalytic units released and activated 1. Signal Transduction involving Gs-Proteins 1.3 Interaction of cyclic AMP with protein kinase A (PKA) C P Protein Protein + ATP + ADP Notes: Phosphorylation of other proteins and enzymes Signal continued by phosphorylated proteins Further signal amplification 1. Signal Transduction involving Gs-Proteins 1.4 Glycogen Metabolism – triggered by adrenaline in liver cells Adrenaline β-Adrenoreceptor adenylate cyclase 1. Signal Transduction involving Gs-Proteins 1.4 Glycogen Metabolism – triggered by adrenaline in liver cells Notes: Coordinated effect: activation of glycogen metabolism inhibition of glycogen synthesis Adrenaline has different effects on different cells e.g. activates fat metabolism in fat cells 1. Signal Transduction involving Gs-Proteins 1.5 Drugs interacting with cyclic AMP signal transduction Theophylline and caffeine - inhibit phosphodiesterases - phosphodiesterases responsible for metabolising cyclic AMP - cyclic AMP activity prolonged 1. Signal Transduction involving Gi-Proteins Notes: Bind to different receptors from those used by Gs proteins Mechanism of activation is identical αI subunit binds to adenylate cyclase and inhibits it Adenylate cyclase is under dual control (brake/accelerator) Background activity due to constant levels of αs and αi Overall effect depends on dominant alpha subunit Dominant alpha subunit depends on receptors activated 3. Phosphorylation Reactions Prevalent in activation and deactivation of enzymes Phosphorylation radically alters intramolecular binding Results in altered conformations NH3 NH3 NH3 O O P O O O O H O P O O O O O Active site Active site open closed 4. Signal Transduction involving Gq Proteins 4.1 Interaction with phospholipase C (PLC) Notes: Gq proteins - interact with different receptors from those recognised by GS and GI Split by the same mechanism to give an αq subunit The αq subunit activates or deactivates PLC (membrane bound enzyme) Reaction catalysed for as long as αq bound - signal amplification Brake and accelerator effect 4. Signal Transduction involving Gq Proteins 4.1 Interaction with phospholipase C (PLC) Active site Active site (closed) (open) DG α α α PIP2 PLC PLC PLC IP3 Active site αq departs (closed) DG α PIP2 α PLC PLC Phosphate IP3 Enzyme Binding deactivated weakened 4. Signal Transduction involving Gq Proteins 4.1 Interaction with phospholipase C (PLC) Reaction catalysed Inositol triphosphate Diacylglycerol (polar and moves (remains in membrane) into cell cytoplasm) Phosphatidylinositol diphosphate (integral part of cell membrane) R= long chain hydrocarbons P = PO32- 4. Signal Transduction involving Gq Proteins 4.2 Action of diacylglycerol Notes: Activates protein kinase C (PKC) PKC moves from cytoplasm to membrane PKC phosphorylates Ser & Thr residues of protein substrates PKC activates enzymes to catalyse intracellular reactions Linked to inflammation, tumour propagation, smooth muscle activity etc Cell membrane Binding DG DG site for DG DG PKC PKC Enzyme Enzyme PKC Active site (inactive) (active) closed Enzyme-catalysed reaction Cytoplasm Cytoplasm Cytoplasm DG binds to DG PKC moves to Induced fit opens binding site membrane active site 4. Signal Transduction involving Gq Proteins 4.4 Action of inositol triphosphate Notes: IP3 is hydrophilic and enters the cell cytoplasm Mobilises Ca2+ release in cells by opening Ca2+ ion channels Ca2+ activates protein kinases Protein kinases activate intracellular enzymes Cell chemistry is altered leading to a biological effect 4. Signal Transduction involving Gq Proteins 4.4 Action of inositol triphosphate Cell membrane IP3 Cytoplasm Calmodulin Calcium Ca++ Calmodulin Ca++ stores Activation Activation Protein Protein kinase P kinase P Enzyme Enzyme Enzyme Enzyme (inactive) (active) (inactive) (active) Enzyme-catalysed Enzyme-catalysed reaction 4. Signal Transduction involving Gq Proteins 4.5 Resynthesis of PIP2 Several steps IP3 + DG PIP2 Inhibition Li+ salts Lithium salts used vs manic depression 5. Signal Transduction - Tyr Kinase Linked Receptors 5.1 Reaction catalysed by Tyrosine Kinase O Tyrosine O H H N C kinase N C Protein Protein Mg+ Protein Protein + ATP ADP OH O P Tyrosine Phosphorylated residue tyrosine residue 5. Signal Transduction - Tyr Kinase Linked Receptors 5.2 Activation and phosphorylation of receptor Ligand Ligand P P P P P P P P P P Signalling protein 5. Signal Transduction - Tyr Kinase Linked Receptors 5.2 Activation and phosphorylation of receptor Notes: Active site on one half of dimer catalyses phosphorylation of tyrosine residues on other half Dimerisation of receptor is crucial Phosphorylated regions act as binding sites for further proteins and enzymes Results in activation of signalling proteins and enzymes Message carried into cell 5. Signal Transduction - Tyr Kinase Linked Receptors 5.3 Signalling pathways 1-TM Receptors Tyrosine kinase inherent or associated Guanylate cyclase Signalling proteins cGMP PLCγ IP3 GAP Grb2 Others kinase IP3 DG PIP3 Ca++ PKC  5. Signal Transduction - Tyr Kinase Linked Receptors 5.4 Example of a signalling pathway Growth factor 1) Binding of growth factor Dimerisation Phosphorylation 2) Conformational change HO HO HO HO PO PO OH OH OH OH OP OP HO OH HO OH HO OH OH OH PO PO PO OP Binding Grb2 SoS Ras and Grb2 SoS Ras GDP Binding of Grb2 and GTP/GDP Grb2 SoS SoS exchange GTP PO PO OP OP PO PO OP OP PO PO PO OP PO PO PO OP 5. Signal Transduction - Tyr Kinase Linked Receptors 5.4 Example of a signalling pathway Ras Grb2 SoS Gene transcription PO OP PO OP PO PO PO OP Raf (inactive) Raf (active) Mek (inactive) Mek (active) Map kinase (inactive) Map kinase (active) Transcription Transcription