Signal Transduction I: Cell Surface Receptor PDF

Signal Transduction I: Cell Surface Receptor HBH Block 2024-25 Biochemistry #Lecture 1 Assoc. Prof. Dr Venkata Suresh Chinni Department of Biochemistry Faculty of Medicine, Biosciences, and Nursing MAHSA University, Malaysia Email: venkatasures...

Signal Transduction I: Cell Surface Receptor HBH Block 2024-25 Biochemistry #Lecture 1 Assoc. Prof. Dr Venkata Suresh Chinni Department of Biochemistry Faculty of Medicine, Biosciences, and Nursing MAHSA University, Malaysia Email: [email protected]  Learning Outcomes On completion of this lecture, you should be able to: 1. define hormone and differentiate it from enzyme. 2. discuss the classification of hormones based on its chemical structure. 3. discuss different hormones based on biosynthesis, storage, secretion , transportation. 4. explain the feed back mechanism that regulates hormone biosynthesis. 5. describe the role of receptors in hormone action. 6. discuss the mechanism of action that produce metabolic or physiological responses.  WHAT ARE HORMONES? ▪Any substances in an organism that carries a signal to generate some sort of alteration of metabolism at the cellular level is called a HORMONE. ▪ It is also called the 1st messenger. ▪ A Hormone Interacts with a specific receptor and Amplifies the specific signal through a 2nd Messenger. ▪What are the 2nd Messengers? ▪There are several types. Three basic types of second messengers Hydrophilic molecules: water-soluble molecules, like cAMP, cGMP, IP3, and Ca2+, that are located within the cytosol Hydrophobic molecules: water-insoluble molecules, like diacylglycerol, and phosphatidylinositols, which are membrane-associated and diffuse from the plasma membrane into the space where they can reach and regulate membrane-associated Receptors. Gases molecules: nitric oxide (NO), carbon monoxide (CO) and hydrogen sulphide (H2S) which can diffuse both through cytosol and across cellular membranes.  CLASSIFICATION OF HORMONES. Hormones as 1st. Messengers 3 Types only Peptide hormones - insulin, glucagon, growth hormone, Interact with human chorionic gonadotropin (hCG), cell surface follicle stimulating hormones (FSH), Receptors to adrenocorticotropic hormone (ACTH), luteinizing hormone (LH) etc. Generate 2nd Messengers. Amino acid-derived hormones - epinephrine, norepinephrine, thyroid hormones. Interacts with Steroid hormones intracellular - aldosterone, cortisol, testosterone, receptors estrogen.  HORMONE INTERACTION WITH RECEPTOR - Classification based on the locations of receptors: 1. Cell surface (in plasma membrane) 2. Intracellular. HYPOTHETICAL Receptor for peptide CELL hormones & amino acid derived hormones Other steroid hormones & related receptor Nucleu Thyroid hormone Cell membrane s receptor Cytoplasm Hormone Steroid hormone receptor Mechanism of Second Messenger Synthesis  GENERAL MECHANISM OF SIGNAL TRANSDUCTION ACROSS CELL MEMBRANE Hormone Receptor G protein Enzyme PLASMA MEMBRANE 2nd messenger Cytoplasmic & nuclear effectors Generate cellular response Hormone binds to cell surface receptor of target cell. → cause conformational changes in receptor, enabling association/ binding with G protein. → activated G protein will cause activation of enzyme. → enzyme then synthesizes intracellular 2nd messenger.  SPECIFITY & REGULATION OF RECEPTOR Important features of the receptors : ▪ high degree of SPECIFICITY - e.g b1 and b2-adrenergic receptors (b1 has a higher affinity for norepinephrine compared to epinephrine). ▪ high affinity - affinity constant in the range of 109 - 1011 M-1. - i.e. very tight binding. ▪ receptors can be REGULATED - e.g adrenergic receptors (when phosphorylated, receptor binds to b arrestin, blocks the receptor’s ability to activate G-protein). ▪ hormone-receptor complex can be internalized (endocytosis).  G PROTEIN G protein is also called a Transducer protein. It transmits external stimuli to effector enzymes. G-protein is made of 3 subunits (a, b, g). - has GTPase activity: hydrolysis GTP → GDP. - exist in 2 conformation : - inactive GDP-bound form. - active GTP-bound form. - a-subunit : - as : a-subunit activates adenylate cyclase. - ai : a-subunit inhibits adenylate cyclase. - Probably the difference between Inhibitory G protein (Gi) and stimulatory G protein (Gs) is due to differences in the subunit structure (as or ai). HORMONE-RECEPTOR INTERACTION: Adenylyl Cyclase Signaling Pathway 1. Resting state Receptor, G-protein & enzyme not interacting with each other. 2. Receptor binds hormone, undergoes conformational change and exposes site for G-protein attachment (G-GDP). 3. Activation of G protein causes the exchange of bound GDP for GTP by a subunit. a-GTP dissociate from abg- complex. 4. a-GTP interacts with enzyme (adenylate cyclase) to activate the enzyme. bg-subunit dissociate from the hormone receptor complex. 5. Activated adenylcyclase converts ATP to cyclic AMP (cAMP). 6. a-Subunit hydrolysed GTP to GDP allows a-GDP to interact with bg- subunits once again (thus, reform the abg-GDP/ G protein).  (i) cAMP – protein kinase A pathway Synthesized by cyclization of ATP, catalyzed by adenylate cyclase. The 3’-OH group of ribose unit attacks the a-phosphoryl group of ATP to form phosphodiester bond. Adenine Adenine PPi Adenylate cyclase ATP Cyclic AMP  Role of cAMP in the breakdown of GLYCOGEN - glucagon and epinephrine/adrenaline in breakdown of glycogen (glycogenolysis) in the liver via protein kinase A. Hormone (glucagon, epinephrine) Receptor ATP cAMP cAMP Inactive cAMP protein kinase A stimulates protein kinase glycogen Active glucose protein kinase A  Role of cAMP in the action of hormones Glucagon and epinephrine/adrenaline breakdown glycogen (glycogenolysis) in the liver via protein kinase A. Hormone (glucagon, epinephrine) Receptor ATP cAMP Phosphodiesterase AMP Insulin Inactive cAMP protein kinase A stimulates protein kinase glycogen Active glucose protein kinase A  EPINEPHRINE (MUSCLE LIVER CELLS) CELL MEMBRANE GLUCAGON (LIVER CELLS) Adenyl cyclase + (inactive) INSULIN + Regulation of glycogen degradation Adenyl cyclase (active) ATP cAMP GLYCOGEN BREAKDOWN Protein kinase A (inactive) Protein kinase A P Covalent modification (active) Glycogen phosphorylase a Phosphate added on (active) serine and threonine ATP ADP P ADP Glycogen phosphorylase kinase Glycogen phosphorylase kinase (inactive) (active) ATP Glycogen phosphorylase b (inactive)  SECOND MESSENGERS - Any compound that acts intra cellularily in response to an extra cellular signal. - Hormones CANNOT ENTER CELL, therefore, REQUIRE A SECOND MESSENGER. - The different types of second messengers : (i) Cyclic AMP (cAMP) - protein kinase A pathway. (ii) IP3, DAG and Ca2+ - protein kinase C pathway. (iii) Cyclic GMP (cGMP) - protein kinase G pathway. (iv) Tyrosine kinase pathway.  (ii) Inositol trisphosphate (IP3), Diacylglycerol (DAG) & Ca2+ – protein kinase C pathway Phospholipase C (PLC) cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) to produce 1,2-diacylglycerol (DAG) and inositol 1,4,5- (PIP2) trisphosphate (IP3). Phospholipase C (PLC) (DAG) (IP3) Enzyme-catalyzed synthesis of DAG and IP3. IP3 and Calcium as Second Messengers  Mode of action of GnRH in the release of FSH and LH Extracellular side ▪ GnRH binds to cell surface GnRH FS LH receptors in gonadotropic cell GnRH receptor H G protein membrane. Cell membrane ▪ Signal is transduced via G- DA protein and phospholipase C PIP PIP2 G + PI (PLC) is activated. PLC Protein Cytosolic side + kinase C Ca2+ ▪ PLC hydrolyzed PIP2 to DAG P and IP3 IP3 + Ca2+ Phosphorylated Ca2+ protein performs Exocytosis specific function Regulation of secretion of LH Endoplasmic reticulum FS Ca2+ storage HLH and FSH  Mode of action of GnRH in ▪ IP3 diffuse to cytosol and binds to ER membrane receptor and the release of FSH and LH Extracellular side stimulates the release of Ca2+. GnRH FSH LH GnRH receptor Receptor G protein ▪ Ca2+ are important in exocytosis Cell membrane by facilitating fusion of secretory granules to the cytoplasmic side of the plasma membrane. DA PIP PIP2 + G PI ▪ Ca2+ will cause the translocation PLC Cytosolic side Protein of PKC to membrane + kinase C Ca2+ P ▪ → PKC activated by DAG. IP3 Phosphorylated + Ca2+ Ca2+ protein performs Exocytosis specific function ▪ PKC phosphorylated protein than participates in exocytosis of LH and FSH from cell. Endoplasmic reticulum FSH Ca2+ storage LH Regulation of secretion of LH and FSH  NO as a 2nd Messenger NO is synthesised from Arginine by action of Nitric oxide synthase NOS. There are 2 endothelial forms of NOS (a) constitutive cNOS type III and an (b) inducible iNOS (type II) In addition to endothelial NOS there is a (c) Neural nNOS (Type I) that serves as a transmitter in the brain and different nerves in the peripheral nervous system including autonomic nerves that innervate penile erectile tissues to produce vasodilation (iii) Nitric Oxide can stimulate production of cGMP Nitric Oxide can stimulate production of cGMP by interacting with the haem group of the enzyme souble guanylate cyclase (sGC). This interaction allows sGC to convert GTP into cGMP. Once produced cGMP can have a number of effects in cells, but many of those effects are mediated through the activation of protein kinase G (PKG). Active PKG is ultimately responsible for many of the effects of Nitric Oxide including its effects on blood vessel relaxation (vasodilation). L-arginine + 3/2 NADPH + H+ + 2 O2 citrulline + nitric oxide + 3/2 NADP+ Role of cAMP, DAG, cGMP Adenyl cyclase converts ATP to cAMP which activates Protein kinase A. Phospholipase C converts PIP2 to IP3 and DAG which activates Protein kinase C. NO activates guanylate cyclase to convert GTP to cGMP which activates Protein kinase G. Endothhelial cells contain Inducible and Constitutive Nitric Oxide synthase Guanylate cyclase Role of cAMP, DAG, cGMP Adenyl cyclase converts ATP to cAMP which activates Protein kinase A. Phospholipase C converts PIP2 to IP3 and DAG which activates Protein kinase C. NO activates guanylate cyclase to convert GTP to cGMP which activates Protein kinase G. Nitric Oxide activates Guanylate Cyclase  Activation of PKG by cGMP Activation of PKG by cGMP leads to activation of myosin phosphatase which in turn leads to release of calcium from intracellular stores in smooth muscle cells. This in turn leads to relaxation of the smooth muscle cells. In the case of vasodilation the Nitric Oxide is originally produced in the neighbouring endothelial cells before diffusing into the smooth muscle cells where it actiavtes sGC and cGMP production. Activation of PKG by cGMP PKG can also have other effects in cells, for example by activating a number of transcription factors which can lead to changes in gene expression which in turn can alter the response of the cell to a variety of stimuli. cGMP can also be converted back to GTP by proteins known as phosphodiesterases. Conversion of cGMP to GTP effectively blocks further Nitric Oxide signalling. There are now several drugs which function as phosphodiesterase inhibitors and can restore Nitric Oxide / cGMP signalling. Perhaps the best known of this class of drugs is Viagra. Nitric Oxide activates Guanylate Cyclase inhibits Viagra (iv) Tyrosine Kinase Pathway Insulin  Receptor  Extracellular Protein kinase system involves phosphorylation of tyrosine. Intracellular Occurs in cytoplasmic domains of PP-tyr tyr- P membrane receptor. Kinase kinase 2nd messenger Important for growth factor receptors: Protein Ser/Thr - Insulin Protein Ser/Thr phosphatase - Epidermal growth factor (EGF) kinase - Platelet derived growth factor (PDGF) - Nerve growth factor (NGF) Protein Protein - Vascular endothelial growth factor phosphorylation dephosphorylation (VEGF) - certain oncogenes. GROWTH METABOLISM glucose uptake Long term effect Short term effect  Hypothetical scheme for signal transduction in insulin action. Insulin  Receptor  Binding of insulin Extracellular - receptor to undergo tyr Intracellular autophosphorylation & subsequently kinase PP-tyr tyr- P activation. Tyr phosphorylation Kinase kinase 2nd messenger - regulating essential cellular process. Protein Ser/Thr Protein Ser/Thr phosphatase kinase ▪ Metabolism reactions Protein Protein - translocation of GLUT4 →  glucose phosphorylation dephosphorylation uptake (muscle, adipose tissue) -  glycogen synthesis GROWTH METABOLISM -  lipid synthesis glucose uptake ▪ Cell growth/death Long term effect Short term effect  SPECIFIC READING MATERIALS 1. Devlin’s Textbook of Biochemistry with Clinical Correlations, 5th edition pp 925-931; 943-953. 2. Lippincott Illustrated review of Biochemistry pp 79-85. 3. Harpers Review of Biochemistry, 25th edition, Chapter 44 (Cell-surface and Intracellular Receptors). Thank you  FACULTY OF MEDICINE MHBH HUMAN BODY IN HEALTH MINERALS ASSOC. PROF. DR. CHIN JIN HAN [email protected] BIOCHEMISTRY MINERALS Learning Outcomes On completion of this topic, students should be able to: 1. Define and classify minerals 2. Explain the requirement of macro minerals such as calcium, iron, magnesium and manganese 3. Explain the requirement of micro minerals such as cobalt, zinc, selenium, chromium and vanadium. BIOCHEMISTRY MINERALS Introduction of Minerals Properties Inorganic substances that have a function in the body. It cannot be synthesised by the body and must be provided in the diet When intake is insufficient, deficiency may develop. Excessive intakes maybe toxic BIOCHEMISTRY MINERAL METABOLISM Introduction of Minerals Functions Cofactors in the enzymatic reactions Osmoregulation to maintain body fluid balance Regulation of acid-base balance. Provide a good medium for the protoplasmic activities (permeability of the cell membrane and normal functioning of the cells, irritability of nerve cells) Classification of Minerals based on Daily Requirement Sodium (Na), Potassium (K), Daily Calcium (Ca), Macrominerals requirement: Magnesium (Mg), >100 mg/day Chlorine (Cl), Phosphorus (P), Sulfur (S) Minerals Iron (Fe), Zinc (Zn), Manganese (Mn), Copper (Cu), Daily Cobalt (Co), Microminerals requirement: Chromium (Cr),