Revision. camp pathway

Transcription

1 االله الرحمن الرحيم بسم

2 Revision camp pathway

3 camp pathway

4 Revision camp pathway Adenylate cyclase

5 Adenylate Cyclase enzyme Adenylate cyclase catalyses the formation of camp from ATP. Stimulation or inhibition of adenylate cyclase depends on the type of activated G protein. hormones activate adenylate cyclase FSH, LH, TSH, HCG. Glucagons. β catecholamines. PTH and calcitonin. hormones inhibit adenylate cyclase Somatostatin. Angiotensin II. α2 catecholamines

6 Revision camp pathway Adenylate cyclase G regulatory proteins

7 G-regulatory protein This protein is so named because it binds to guanine nucleotides: GDP or GTP. It consists of 3 polypeptide subunits (heterotrimeric protein): α subunit, β subunit and γ subunit protein): α subunit, β subunit and γ subunit Under basal conditions the α subunit binds to GDP Binding of the hormone to its receptor activates G protein through: Exchange of GDP and GTP on the α subunit. Dissociation of active α subunit from β- γ subunits.

8 A. G-regulatory protein The active α subunit (α-gtp) affects the activity of the next reaction according to the type of G protein: Gs: Stimulates adenylate cyclase. Gi: Inhibits adenylate cyclase. Gq: Stimulates phospholipase C. Other types affect Ca channels and K channels. The α subunit has intrinsic GTPase activity. After α subunit exerts its effects, GTPase hydrolyses its GTP into GDP and Pi. The inactive α subunit (α GDP) reassociates with the β- γ subunits and remains inactive until reactivated again.

9 Revision camp pathway Adenylate cyclase G regulatory proteins PKA

10 Protein Kinase A camp dependent protein kinase A is a tetramer of: 2 regulatory subunits (R). 2 catalytic subunits (C). The R2C2 tetramer is inactive. On activation 4 camp molecules bind to the 2 regulatory subunits leaving the 2 catalytic subunits free to act. Active protein kinase transfers gamma phosphate group from ATP to serine or threonine amino acid residues of a specific protein causing its phosphorylation. The phosphorylated protein e.g. enzyme, mediates the hormonal effect.

11 Revision camp pathway Adenylate cyclase G regulatory proteins PKA

12 Dr. Hani Alrefai

13 ILOs Hormones acting through calcium signaling Calcium signaling pathway Calmidulin Mechanism of action of insulin Mechanism of action of GH

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15 Calcium or/and phosphatidyl inositols The hormones which use these second messengers include: Gonadotropin releasing hormones (GnRH) Thyrotropin releasing hormone (TRH) Antidiuretic hormone (ADH) α1 adrenergic catecholamines

16 Calcium or/and phosphatidyl inositols Gq PLC PKC

17 Calcium or/and phosphatidyl inositols Binding of the hormone to its specific receptor activates a specific type of G protein (Gq). The active G protein activates the enzyme phospholipase C (PLC). The active PLC hydrolyses phosphatidyl inositol 4,5 biphosphate (PIP2) to: 1,2 Diacyl glycerol (DAG). Inositol Triphosphate (IP3).

18 Calcium or/and phosphatidyl inositols 1. DAG: It activates protein kinase C. Active protein kinase C phosphorylates specific substrates e.g. enzymes which mediate the effects of the hormone. 2. IP3: It releases Ca2+ from intracellular storage sites: Mitochondria. Endoplasmic reticulum.

19 Calcium or/and phosphatidyl inositols Intracellular Ca2+ could be increased by: 1. Intracellular storage sites: IP3. 2. Extracellular calcium: Membrane Calcium channels. Some hormones when bound to their receptors stimulate certain type of G protein that leads to opening of these channels.

20 Calcium or/and phosphatidyl inositols 4 Ca2+ molecules bind to calmodulin to form Ca2+/ calmodulin complex. Ca2+/calmodulin complex can change the activity of certain enzymes. These enzymes mediate the effects of the hormone N.B. Ca2+ /calmodulin complex regulates some structural elements in the cell e.g. Actin-myosin complex of smooth muscles. Microfilament-mediated processes e.g. mitosis and endocytosis.

21 Calcium or/and phosphatidyl inositols Calmodulin: It is a calcium dependent regulatory protein. It is a 17 Kilo Dalton protein. It is structurally similar to muscle protein troponin C. Calmodulin has 4 Ca2+ binding sites.

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23 Protein Kinase Cascade Tyrosine kinases: group of enzymes, which phosphorylate their substrates on tyrosine residues. Tyrosine kinase may be: 1. Intrinsic part of the receptor. 2. Intracellular associated with the receptor.

24 1- Receptor with intrinsic tyrosine Kinase e.g. insulin receptor. 1 Binding of the hormone to its receptor 2 Activation of tyrosine kinase receptor 3 4 Auto-phosphorylation Phosphorylation of Insulin Receptor Substrates (IRS) on tyrosine residues. 5 Activate Phosphatidyl inositol 3 kinase (PI3-kinase): Activate Mitogen Activated Protein Kinase Cascade (MAP Kinase Cascade).

25 Activate Mitogen Activated Protein Kinase Cascade (MAP) IRS RAS RAF MEK MAP kinase The active MAP kinase affects certain transcription factors and ribosomal subunits leading to alteration of protein transcription. which mediate the effects of the hormone. RAS is a G protein with intrinsic GTPase activity. The other are serine/threonine kinases.

26 2- Receptor with intracellular associated intrinsic tyrosine Kinase e.g. Growth hormone, prolactin, interferon and erythropoietin 1 Binding of the hormone to its receptor 2 3 Activation of the associated tyrosine kinases (JAK kinases or TYK kinases ) Phosphorylation of the receptor. Phosphorylation of the enzyme itself. IRS MAP 4 Activation a number of signaling pathways PLC Signal Transiducers and Activators of Transcription (STAT)

27 Signal Transiducers and Activators of Transcription (STAT) STAT proteins are cytosolic proteins. The phosphorylated STAT: Translocate to the nucleus. Bind to specific DNA element. Activate transcription

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