hormones lecture h04 h05
TRANSCRIPT
HormonesInsulin (RTK) Signaling
Dr. Aga Syed SameerCSIR Lecturer (Demonstrator)Department of Biochemistry,Medical College,Sher-I-Kashmir Institute of Medical Sciences, Bemina, Srinagar, Kashmir, 190010. India.
First MBBS
Lecture No: H 04
Time : 10:00am
Dated: 12/03/2015
• Insulin:
Insulin is anabolic hormone favoring synthesis of glycogen, TGAs and Protein
Insulin has a half life of 6 minutesProduced by β cells of Islets of Langerhans
Degraded by Insulinase (Liver)
• Insulin:
Insulin is dipeptide – one α Chain and One β Chainα Chain has 21 aas
β Chain has 30 aas
Two Disulfide linkages hold them together, with one extra in α Chain 6-11 with in α Chain
7-7 and 20-19 with α Chain and β Chain
Receptor Tyrosine Kinases
• Insulin: Insulin is antagonist to Glucagon in its function
Both hormones however respond to changes in blood glucose levels
↑ levels of Blood Glucose cause β-cells of pancreas to secrete Insulin
It functions as extracellular messenger molecule; informing cells that blood glucose levels are higher
Cells respond to Insulin by increasing Glucose uptake from the blood
Additionally, Insulin also causes its effects on metabolism as:↑ Glycogen Synthesis: Activating Glycogen Synthase Via GSKβ1
↑ Triglyceride Synthesis
↓ Gluconeogenesis: Deactivating Glycogen Phosphorylase
Receptor Tyrosine Kinases
• Insulin Receptor (IR):
• Is hetero-tetramer –
Two α & two β subunits
• α-Chain:
Extracellular: Insulin Binding Site
• β-Chain:
Extracellular : Bound to α-Chain
Single Trans-membrane part
Cytoplasmic Part: Tyrosine Kinase Domain
Insulin receptor half-life is only 7 hours
Receptor Tyrosine Kinases
• Single molecule of Insulin binds to Insulin Receptor for activation
• Binding causes Dimerization of IR by repositioning of the ligand binding domains of the α-chain on the outside of cell
• Then Tyrosine Kinase Domain of the Cytoplasmic Part of β-Chains come into close proximity (Juxtapositioning)
• This results in Trans-Autophosphorylation of the both β-Chains at several critical tyrosine residues;
• Thereby activating IR.
Insulin Receptor (IR)
• Phosphorylation occurs critically in the three tyrosine residues of Activation Loop of β-Chain.
• Important “Tyrosine” of RT is 960. Until and unless its phosphorylation occurs no signal cascade is created downstream
• Phosphotyrosine residues in turn act as Docking sites for the downstream proteins of the signal cascade
• The Phosphorylation causes conformational change in Activation Loop of β-Chain leaving catalytic cleft open for substrate binding.
Insulin Receptor (IR)
Insulin Receptor (IR)
• Activated “IR” then associates itself with Intracellular Effector Proteins - “Insulin Receptor Substrates” (IRSs) : IRS1 & IRS2
• IRSs have three Domains:• PH domain - N Terminal
• PTB Domain
• Tail containing Tyrosine Phosphorylation Sites
• The IRSs bind to IR via its Phosphotyrosine Binding (PTB) Domain
• IRSs on activation provide docking sites for all SH2-Domain Containing signaling proteins: PI3 Kinase, Grb2, PDK1
• The activated IRSs then interact with Phospholipids present on the inside of the Plasma Membrane
Insulin Receptor (IR)
Insulin Receptor (IR)
• PI3 Kinase has two subunits:• One contains two SH2 domains with which it binds to
Phosphorylation sites of Inositol of Phosphatidyl Inositol Other contains Catalytic site which causes phosphorylation of bound Inositol.
• PI3 Kinase is activated on binding with the PH Domain of Activated IRS1/2
• It function to phosphorylate the membrane bound PhosphatidylInositol Phosphates (at 3’ position of sugar) resulting finally in the production of PI-(3,4,5)P3
• PI-(3,4,5)P3 in turn mediates the function of Insulin signaling in regulating the blood Glucose Levels.
PI3Kinase (PI3K)
PI3Kinase (PI3K)
PI 3 Kinase products
(relevant to insulinsignallingis the production of PI-3,4,5-P3)
• Increased concentration of PIP3 recruits Protein Kinase B (PKB/Akt) to the membrane of the cell
• PKB is then phosphorylated by two membrane associated kinases PhosphoInositol Dependent Kinases (PDK1) and/or PKC
• Activated PKB is then released into the cytosol
• Causes phosphorylation of many proteins at Ser/Thr residues
• Helps in the translocation and fusion of GLUT4 containing vesicles with the plasma membrane via Rab4 protein
• GLUT4 then transports the Glucose from the blood into the cell
PI3Kinase (PI3K)
Protein Kinase B (PKB)
Rab4
PKB & GSK
PKB & GSK
AssignmentPatho-physiology of Diabetes Type IIInsulin and GlucagonHypo and HyperglycaemiaTypes of HypoglycaemiaInsulin Secretion and Signaling in Hypo/Hyperglycaemia
Effects of InsulinCross talk with other Signals – cAMP; Calcium; Leptin; Management of TD II
HormonesCalcium Signaling
Dr. Aga Syed SameerCSIR Lecturer (Demonstrator)Department of Biochemistry,Medical College,Sher-I-Kashmir Institute of Medical Sciences, Bemina, Srinagar, Kashmir, 190010. India.
First MBBS
Lecture No: H 05
Time : 10:00am
Dated: 12/03/2015
Calcium
• Extracellular calcium concentration is 5mM/L
• Intracellular free/ionized calcium concentration is very low ~0.05-10.0 uM/L
• Substantial amounts of calcium are associated with intracellular organelles such as Endoplasmic Reticulum & Mitochondria
• Inspite of this large concentration gradient & a favorable trans-membrane electrical gradient ; calcium is restrictedfrom entering the cell
Calcium Homeostasis
• Four calcium channels (mainly) play a critical role in regulating the calcium levels in the cytosol
• Two are highly functional in basal conditions
• Na+/Ca2+ channel in plasma membrane
• SERCA in Smooth Endoplasmic Reticulum
• Two are activated and in use under hormone or neurotransmitter action
• Voltage dependent Ca2+ channels in Plasma Membrane
• Ryanodine Receptors in Smooth Endoplasmic Reticulum
• There are three ways of changing the cytosolic calcium concentration:
By activating the receptors that serves as the channels (ligandgated Ca2+ channels) in the plasma membrane of the cell by hormone signaling.
Indirectly promoting the calcium influx by modulating the membrane potential at the plasma membrane, inturn opens the voltage gated Ca2+ channels.
Ca2+ can be mobilized from ER and also from mitochondrial parts
• Hormone action via Ca2+ involves the mediation of intracellular targets of Ca2+ ; which are Ca2+ - dependent regulator of “phosphodi-esterase /kinase activity”
Calcium Homeostasis
Calcium Homeostasis
Calmodulin – The Mediator• Is a Ca2+ - dependent regulatory protein
• 17kDA protein: Homologous to muscle protein troponin C in structure & function
• It has four Ca2+ - binding sites & full occupancy of these sites leads to a marked conformational change
• This allows calmodulin to activate Enzymes & Ion channels
• The interaction of Ca2+ with calmodulin is similar to the binding of cAMP to PKA and the subsequent activation of this molecule
• Calmodulin mediates its action via CaMKinase
Calmodulin
• Calmodulin is particularly involved in regulating various Kinases and Enzymes of cyclic nucleotide generation & degradation
• In addition, Ca2+/Calmodulin regulates the activity of many structural elements in cells:
• Actin-Myosin complex of smooth muscles
• Micro-filament mediated processes
• Mitosis
• Granule release
• Endocytosis
Calmodulin
• Number of critical metabolic enzymes are regulated by Ca2+, Phosphorylation /Both:
Glycogen Synthase;
Pyruvate Kinase;
Pyruvate Carboxylase;
Pyruvate Dehydrogenase;
Glycerol 3 Phosphate Dehydrogenase
Signaling• Hormone/Ligand activates GPCRs and Gq which inturn
activates PLCβ1
• IP3 and DAG activate Protein Kinase C
• PKC activity is inturn affected by calcium concentration in cytosol
• IP3 interacts with specific receptors (Ryanodine Receptors) and release calcium from SER into cytoplasm
• The activation of PKC and Increased calcium concentration activates “Ca2+ - Calmodulin Dependent Kinases (CaMK)” which mediates its effect
Ca2+/Calmodulin
Ca2+ Signaling in Synapse
Questions?