Cell signalling. Link Teaching ; Ľ. Tomáška, Department of Genetics

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1 Cell signalling Suggested reading: Reese et al. (2013) Campbell Biology. Sadava & Hills (2012) Life: The Science of Biology. Chapters on cell signalling Link Teaching ; Ľ. Tomáška, Department of Genetics

2 Useful www links: MIT Open courses: Biology/index.htm Nobel prize lectures: TED lectures: ibiology:

3 The Central dogma of molecular biology describes the direction of flow of genetic information DNA RNA protein function function

4 A metaphoric representation of the Central dogma is decoding of a digital message Coded instructions Decoder Interpretation

5 However, this metaphor cannot explain ambiguity of genetic information Coded instructions Decoder Interpretation

6 Interpretation of the encoded information is context-dependent x9

7 Interpretation of the encoded information is context-dependent x9

8 Interpretation of the encoded information is context-dependent x7

9 Interpretation of the encoded information is context-dependent DNA modifications DNA-protein interactions Gene expression Cell structures Cell signalling...

10 Cell signalling is an important tool for expression of genetic information CONTEXT Cell signalling Tissues/cell communities Cells Cell structures Gene expression DNA-protein interactions DNA CONTEXT

11 Cells are constantly exposed to a wide variety of signals Sadava & Hills (2012). Life: The Science of Biology.

12 Sadava & Hills (2012). Life: The Science of Biology. These signals come from both external and internal envirobments

13 Caffeine is one of the environmental signals affecting our cells Coffee 180 mg / cup Tea 90 mg / cup Coca-Cola 50 mg / cup Chocolade 20 mg / cup

14 Signals from the environment affect our cells by imitating natural chemicals produced by the body adenosine caffeine

15 Correct interpretation of the signals is essential for appropriate cellular decisions External factors Cell division Nutrients Growth factors Temperature Internal factors Stage of the cell cycle Genotype DNA damage Metabolc state Cell line Quiscience Differentiation Senescence Apoptosis

16 Gap junctions mediate direct cell-to-cell communications Sadava & Hills (2012). Life: The Science of Biology. Plasma membranes (2 nm)

17 In most cases the cell-cell communication takes place over longer distances 1. Binary choice + signal - signal - signal

18 In most cases the cell-cell communication takes place over longer distances 2. Cell fate can depend on the concentration of the signal

19 In most cases the cell-cell communication takes place over longer distances Cell signalling can mediate formation of patterns during ontogenesis Gradient model Relay model

20 There are various forms of cell signalling CONTACT DEPENDENT Signal Receptor

21 xistujú viaceré formy komuniácie medzi bunkami CONTACT-DEPENDENT Signal PARACRINE / AUTOCRINE Receptor SYNAPTIC ENDOCRINE Synapse

22 he forms of communications between cells can e compared with the following means of interersonal communications: Phone conversation Communication with people at the hotel reception Statement in the radio Talking to oneself SYNAPTIC PARACRINE ENDOCRINE AUTOCRINE

23 Cell signalling pathways exhibit several universal characteristics Ligand (first messenger) Receptor Efector Second messenger Signal transducer Characteristics: Specificity Arrangement in a cascade Amplification( ) Robustness Networking

24 Multicellular bodies produce a large number of ligands affecting the target cells via their binding to specific receptors Neurogenesis Growth of axons and dendrites Formation of synapses

25 Growth of neurons is under the control of a chemical signal Control +signal

26 What is the nature of the signal? Rita Levi-Montalcini ( ) Paola Levi-Montalcini ( )

27 The active substance is a polypeptide called (neuronal growth factor, NGF) Stanley Cohen (1922-)

28 Growth factors are also involved in navigation of axonal growth during neurogenesis dendrite cell body Axon growth cone Fluorescently stained actin

29 Growth factors are also involved in navigation of axonal growth during neurogenesis CHEMOATTRACTION

30 How is it possible to quantitatively express the specificity of the receptor-ligand binding?

31 The affinity of a receptor to a ligand is expresses as a dissociation constant K D [H 3 ] Bound ligand (cpm/mg protein) K D e.g. Insulin: K D = 14 nmol.dm -3 number of receptor: 33,000 per cell Ligand concentration

32 The binding of ligands to their receptors occurs spontaneously, if it is associated with a release of free Gibbs energy (i.e. ΔG < 0) ΔG = G B - G A Free Gibbs energy (G) A B ΔG > 0 B A ΔG < 0 Requires an input of energy Spontaneous reaction

33 Specific binding of a protein (P) to a ligand (B) is mediated by a greater net free energy change compared to a nonspecific binding to a ligand (A) P A B Free energy G P A P B ΔG B ΔG A ΔG specific

34 Specificity of binding can be quantified in a form of a dissociation constant (K D ) [R] + [H] k on k off [RH] At equilibrium: K D = k off k on K D = [R][H] [RH]

35 Specificity of binding can be quantified in a form of a dissociation constant (K D ) that can be calculated from a binding curve [H 3 ] ligand bound (cpm/mg protein) K D Ligand concentration [M, mol.dm -3 )

36 There is a relationship between dissociation constant (K D ) and free energy of association (ΔG association ) K D [M] ΔG association = RT lnk D ΔG association (kj/mol)

37 There is a relationship between dissociation constant (K D ) and free energy of association (ΔG association ) K D [M] ΔG association = RT lnk D ΔG association (kj/mol)

38 Small differences in two molecules can have a dramatic consequences on their binding properties Example: a single hydrogen bond can have a free energy value of kj/mol, so addition or subtraction of a single hydrogen bond can affect the K D by several orders of magnituted K D [M] ΔG association (kj/mol)

39 The binding curve is helpful in determination of both K D and the number of binding sites (e.g. receptors) [H 3 ] ligand bound (cpm/mg protein) K D e.g. Insulin: K D = 14 nmol.dm -3 Number of IR: 33,000 per cell Ligand concentration

40 Kinetic parameters of the ligand-receptor interaction are finely tuned to mediate appropriate cell response [RH] K D Cell response [H] Adrenaline/Epinephrine: K D = 5 µm [Adrenaline] <<0.5 µm

41 Changes in kinetic parameters of the ligand-receptor interactions can result in pathological states Kennedy disease (spinal and bulbar myotonic atrophy) I 1 2 II III IV 1 Kennedy et al. (1968). Neurology. 18:

42 Patients with Kennedy s disease exhibit changes in K D of androgen receptor K D (normal) = /-0.06 nmol.dm -3 K D (patient) = /-0.17 nmol.dm -3 MacLean et al. (1995). J. Clin. Endocrinol. Metabol. 80:

43 Information about kinetic parametrs of ligand-receptor interaction is important for a preparation of clinically important drugs Ligand agonist- antagonist adrenaline isoproterenol - alprenolol K D / response: Adrenaline: 5x10-6 M / camp Isoproterenol: 0.4x10-6 M / camp Alprenolol: x10-6 M /---camp

44 Binding of a ligand to a receptor induces a series of biochemical reactions

45 One of these reactions is production of small molecules called second messengers Sadava a kol. (2007). Life: The Science of Biology. Sinnauer Ass.

46 One of these reactions is production of small molecules called second messengers Sadava a kol. (2007). Life: The Science of Biology. Sinnauer Ass.

47 Cyclic adenosine monophosphate (camp) is a typical second messenger Sadava a kol. (2007). Life: The Science of Biology. Sinnauer Ass.

48 Another types of reactions triggered by activated receptors are various reversible post-translational modifications of proteins Phosphorylation (-PO 4-3 ) Methylation (-CH 3 ) Acetylation (-COO - )...

49 Phosphorylation is catalyzed by special family of enzymes called kinases ATP + X X: kinase sugars polynucleotides Inositol ring in phospholipids Ser, Thr, Tyr, His, Arg residues in proteins X-P ADP P i phosphatase X

50 The most frequent phosphoamino acids Fosfoserín Fosfotreonín Fosfotyrozín Fosfohistidín

51 Phosphorylation may affect biochemical properties of a protein isocitrate dehydrogenase

52 Binding of insulin released from pancreatic β-cells to its receptor on the host cells induces release of glucose

53 One ligand can induce several cellular responses Response 1 Response 2 Response 3 Response 4 Response 5

54 One ligand (such as acetylcholine) can induce several cellular responses receptor

55 Dictyostelium discoideum A simple model of cellular differentiation aggregation nutrients slug Stalk Stalk

56 Dictyostelium discoideum A simple model of cellular differentiation

57 Coordinated behaviour of D. discoideum is possible due to their ability to measure cell concentrations (quorum sensing) Production of autoinducer Induction of cellular response in the neighboring cells Coordinated action of all members of the cell population AGGREGATION

58 Signalling pathways are arranged in networks containing simple elements Negative feedback Positive feedback Feedforward relay Stimulatory crosstalk Inhibitory crosstalk

59 Signalling pathway mediating aggregation of Dictyostelium contains several feedback loops 5 AMP 5 pulse camp RECEPTOR GENE EXPRESSION

60 Signaling networks exhibit non-intuitive cell bebaviour camp camp (pmol/mg of proteínu/min protein/min) Time (min) Čas (min)

61 Barabási, A.L. (2002). Linked. Perseus Publishing. Analysis of networks is an important approach to understand complex systems C c d g A e D a b f B

62 Analysis of networks is an important approach to understand complex systems

63 A detailed description of cell signalling pathways/networks willbe instrumental in a construction of a vrtual cell

64 Biology+ +chemistry+mathematics+informatics Systems biology

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