Diapositive 1

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The Ras MAP kinase pathway
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The big family of Receptor Tyrosine Kinases
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Receptor domain architecture and receptor
activation by EGF (TGFa)
unusual mode of allosteric activation, formation
of an asymmetric dimer, followed by
trans-phosphorylation of the C-tails
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Receptors cannot dimerize because their
dimerization arms (domain-II) are buried within
the molecule (bound to domain IV)
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The dimerized receptor interaction between
II-domains ( dimerization arms )
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Detail of the trans-phosphorylation reaction of
C-terminal tails by dimerized EGF receptors
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Phophorylated tyrosines and their surrounding
amino acids form docking sites for adaptor- and
effector proteins
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Different ligands, different receptors and
different receptor-combinations, with different
affinities for interaction with adaptor- or
effector proteins
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A) When large scale micro-array protein
interaction protocoles are applied,  the tough
gets going . This picture illustrates the
 interactome  of different phosphorylated EGF
receptor C-terminal tails B) Note that with
ERBB2, interactions vary greatly with increasing
concentrations of cytoplasmic tails (i.e.
overexpression of ERBB2 may change signalling
patterns). Image from Jones et al. Nature
2006439168-174)
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Domain architecture of adaptor-, docking- and
effector proteins
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Different protein-protein interaction domains
drive the assembly of receptor signalling
complexes
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Branching of signal transduction pathway
(signalling network)
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Sos mediates guanine nucleotide exchange by
widening the nucleotide binding pocket and by
hindering Ser 17 (inside the circle) to interact
with GDP.
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Activation of Ras means rearranging the switch
regions through the tight link between threonine
35 (in pink) and the third (g)-phosphate of ATP.
This rearrangement creates favourable interaction
sites with effectors
Effector loop no interaction
interaction with Raf-RBD effector loop
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Raf binds to the Ras effector loop (aa 32-40)
with its Ras-binding domain (RBD). The image
below shows how the switch-II region of RasGDP
hinders the interaction with Raf
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RasGTP induces a cascade of phosphorylation
reactions, in which each kinase activates the
other by phosphorylation of residues in the
activation segment. ERK2 dimerizes and enters the
nucleus Exactly how Raf is activated and how
ERK2 enters the nucleus remains uncertain
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MEK activates MAPkinase by phosphorylation of
Thr183 and Tyr185. MEK is a rather unusual
protein kinase because of its highly restricted
choice of substrates
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Activated ERKK2 enters the nucleus and
phosphorylates transcription factors. In the case
of Elk-1 this leads to dimerization with SRF
whereas in the case of c-Fos this results in a
prolonged half-life and thus more effective
induction of transcription. With respect to the
cell division cycle, expression of cyclinD is one
of the consequences of the action of ERK2.
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ERK2 is a member of a large family of
mitogen-activated protein kinases (MAPK) which
share sequence identity as well as mode of
activation
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ERK2, as well as other members of the MAPK
family, phosphorylates and activates yet other
protein kinases. These too constitute a family,
the MAPK-activated protein kinases.
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MNK1, MAP-kinase interacting kinase, is
phosphorylated and activated by ERK2. It binds
the eukaryotic initiation factor eIF-4E and
eIF-4G. MNK1 phosphorylates eIF-4E and this
facilitates the association of eIF-3, an
essential protein for the assembly of the
ribosomal complex
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One of the genes induced by the MAPkinase pathway
is the dual specificity phosphatase MKP-1. It
dephosphorylates and de-activates MAPK, both in
the nucleus and the cytoplasm, on its thr-tyr
residues
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The Ras-ERK signal transduction pathway in other
species
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Ras-ERK and development of the ommatidium in
Drosophila (rhabdomere formation)
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Ras-ERK and the development of the vulva in
Caenorhabdites elegans