Signal Transduction: Information Metabolism. Chem 454: Regulatory Mechanisms in Biochemistry University of Wisconsin-Eau Claire

Transcription

1 Signal Transduction: Information Metabolism Chem 454: Regulatory Mechanisms in Biochemistry University of Wisconsin-Eau Claire

2 Introduction Information Metabolism How cells receive, process and respond to information from the environment. A large number of proteins are involved in information processing Signal-transduction cascades Molecular circuits that detect, amplify, integrate external signals. Produce changes in enzyme activity, gene expression or ion channel activity. 2

3 Overview Signal transduction depends on molecular circuits 3

4 Overview Transferring information from the cell s exterior to it s interior involves Primary messenger Cell surface receptors Formation of a receptor-ligand complex Production of a second messenger within the cell This is transduction 4

5 Overview Examples of second messengers 5

6 Overview Protein phosphorylation can occur in response to the second messenger. Tyr Tyr 6

7 Overview Signal termination Without signal termination, cells lose their responsiveness to the signal Some cancers are associated with the inability to properly terminates signals 7

8 Overview Essentially every biochemical process in a cell is a component of a signaltransduction pathway or can be affected by one. 8

9 1. Seven-Transmembrane-Helix Receptors The seventransmembrane-helix receptors (7TM) contain a bundle of 7 α-helices, which span the cell membrane 9

10 1. Seven-Transmembrane-Helix Receptors The seventransmembranehelix receptors (7TM) respond to a wide range of primary messengers 10

11 1.1. Ligand Binding to 7TM Receptors For β-adrenergic receptors, ligand binding to 7TM receptors leads to the activation of G-proteins HO HO H H N CH3 HO epinephrine (adrenaline) 11

12 1.2. G-Proteins G-Proteins cycle between GDP- and GTP-bound forms 12

13 1.2. G-Proteins G-Proteins cycle between GDP- and GTPbound forms 13

14 1.2. G-Proteins G-Proteins cycle between GDP- and GTPbound forms 14

15 1.2. G-Proteins There are many types of G-proteins 15

16 1.3. Activated G Proteins Activated G-proteins transmit signals by binding to other proteins. For example, with the β-adrenergic receptors, the activated G-protein (α-subunit) binds to, and activates, the enzyme adenylate cyclase. Adenylate cyclase catalyzes the synthesis of cyclic- AMP from ATP Cyclic-AMP is a second messenger 16

17 1.4. Resetting G Proteins G-proteins spontaneously reset themselves through GTP hydrolysis 17

18 1.4. Resetting G Proteins For β-adrenergic receptors, prolonged exposure to epinephrine leads to desensitization of the receptor by β-arrestin 18

19 1.5. Cyclic-AMP Cyclic-AMP stimulates the phosphorylation of many target proteins by Protein Kinase A Processes that are stimulated include Enhanced degradation of storage fuels Increased secretion of acid by gastric mucosa Diminished aggregation of blood platelets Opening of chloride channels 19

20 1.5. Cyclic-AMP Phosphorylation of enzymes can turn them off or on. Tyr Tyr 20

21 2. Phopholipase C Activation of the enzyme phospholipase C by a G-protein produces two other second messengers Phospholipase C cleaves phosphotidyl inositol 4,5 bisphosphate to produce inositol 1,4,5-trisphosphate diacylglycerol 21

22 22 2. Phopholipase C

23 2.1. Inositol 1,4,5-Trisphosphate Inositol 1,4,5-trisphosphate opens channels to relases calcium ions from intracellular stores The Ca ++ is released by the stores in the endoplasmic reticulum or the sarcoplasmic reticulum (smooth muscle) The Ca ++ triggers smooth muscle contraction, glycogen breakdown, and vesicle release 23

24 2.2. Diacylglycerol Diacylglycerol activates protein kinase C 24

25 3. Calcium Ion Calcium ion is an ubiquitous cytosolic messenger The cytosolic centraction of Ca ++ ion can by changed very rapidly. The cytosolic concentration (100 nm) is very low compared to the extracellular concentration (5 mm) Ca ++ can bind tightly to proteins 25

26 3.2. Calmodulin Calcium (second messenger) activates the regulatory protein calmodulin Calmodulin contains a couple of EF-hand calcium ion binding motifs 26

27 3.2. Calmodulin Binding calcium converts calmodulin to an active form 27

28 3.2. Calmodulin The active form of calmodulin binds to and alters the activity of a wide range of cellular proteins 28

29 3.2. Calmodulin Calmodulin activates the calciumdedpendent protein kinase (CaM kinase I) by binding to a C- terminal α- helilx 29

30 4. Cross Phosphorylation Some receptors dimerize in response to ligand binding The dimerization brings together protein kinases that are associated with the intracellular domains of the receptors. The protein kinases are then activated by cross-phosphorylization 30

31 4. Cross-phosporylation Example: Human growth hormone Dimerizes the human growth hormone receptor Which in turn, activates Janus kinase 2 (JAK2) 31

32 4. Cross-phosporylation Example: Human growth hormone Dimerizes the human growth hormone receptor Which in turn, activates Janus kinase 2 (JAK2) 32

33 4. Cross-phosporylation Example: Human growth hormone Dimerizes the human growth hormone receptor Which in turn, activates Janus kinase 2 (JAK2) 33

34 4. Cross-phosporylation The JAK 2 kinase has a modular domain structure: 34

35 4. Cross-phosporylation The SH2 domain is a regulatory domain that binds to phosphotyrosinecontaining polypeptides: 35

36 Problem Learn more about the SH2 domain: The Structural Insights module on SH2 domains describes some of the determinants of SH2 specificity and the ways in which SH2-phosphotyrosine binding can affect protein function. Given that the Src kinase SH2 domain bind Src Phophotyrosine 527, what effect do yo think mutation of Glu 529 to Asn would have on th protein kinase activity of Src? Suppose you now obtained a second mutation within Src that reversed the effect of the first. Can you predict what that second mutation might be? 36

37 4. Cross-phosporylation When activated, JAK2 phosphorylates other proteins The growth hormone receptor STAT5, which regulataes gene expression 37

38 4. Cross-phosporylation Activation of growth hormone receptor by JAK2 38

39 4. Cross-phosporylation Activation of the STAT5 gene regulator protein by JAK2 39

40 4.1. Tyrosine Kinase Receptors Some receptors contain tyrosine kinase domains within their covalent structures The epidermal growth factor receptor is an example 40

41 4.1. Tyrosine Kinase Receptors The EGF signal transduction pathway includes a number of players. 41

42 4.1. Tyrosine Kinase Receptors The Grb-2 adaptor protein contains an SH2 and two SH3 domains 42

43 4.1. Tyrosine Kinase Receptors The Grb-2 adaptor protein contains an SH2 and two SH3 domains 43

44 4.1. Tyrosine Kinase Receptors The Sos proteins facilitates the exchange of GTP for GDP in the Ras Protein 44

45 4.2. Ras Protein The Ras protein is a member of a superfamily of monomeric G-proteins 45

46 5. Signaling Defects and Disease Defects in signaling pathways can lead to cancer Cancer is associated with uncontrolled cell growth. Cancer is strongly associated with signal transduction proteins 46

47 5. Signaling Defects and Disease Example Rous Sarcoma Virus codes for a protein, v-src, which is homologous to the cellular, c-src. Rouse Sarcoma Virus produces sarcomas in chickens The v-src protein induces cell transformation, whereas the c-src normally does not. 47

48 5. Signaling Defects and Disease The c-src contains an SH2, an SH3 and a tyrosine kinase domain. 48

49 5. Signaling Defects and Disease The inactive c-src can be activated in three different ways 49

50 5.1. Protein Kinase Inhibitors Protein kinase inhibitors may be effective anticancer drugs 90% of patients with chronic mylogenous leukemia (CML) have a specific chromosomal defect that results in a mutant protein kinase (bcr-abl) that is expressed in levels higher than they should be. Research into protein kinase inhibitors is showing probmise 50

51 5.1. Protein Kinase Inhibitors Protein kinase inhibitors may be effective anticancer drugs 51