Receptor TYROSINE kinases (some recap)

Question 1

What basic mechanism is used by receptor kinases (serine threonine or tyrosine)

Answer 1

Dimerization

Question 2

What type of receptor would induce a SMAD signaling pathway?

Answer 2

TGFbR

Question 3

Briefly describe the SMAD signaling pathway

Answer 3

(NOT TYROSINE KINASE) TGFb binds as a dimer to heterodimeric receptor.
Type 2 receptor phosphorylates Type 1 receptor (serine residue)
Type 1 receptor phosphorylates and activates SMAD2.
SMAD2 binds further SMAD, SMAD4.
Exposing NLS, go to nucleus and be Transcription factor

Question 4

How is SMAD signaling turned off?

Answer 4

SMAD3/4 complex has gene product = SMURF (smad ubiquitination complex)
also phosphatase for SMAD (signal is technically ratio of phosphorylated to unphosphorylated smad)

Question 5

Briefly describe JAK STAT signaling pathway

Answer 5

Cytokine binds 2 identical monomers on membrane. = dimerization
Dimerisation brings tog the two associated kinase domains (JAKs)
JAKs crossphosphorylate = activated
Activated JAK phosphorylates intracellular domain of receptor
SH2 domain on STAT (transcription factor) recognises phosphorylated-tyrosine on receptor and binds.
JAK phosphorylates STAT (SH2 domain)
Phosphorylated STAT recognises second phosphorylated STAT (via p-tyr) and dimerise
Dimerised STATs have intact NLS and go to nucleus to act as a TF

Question 6

What is an example of a ligand that would induce the JAK STAT signaling pathway?

Answer 6

Growth hormone

Question 7

How is JAK STAT signaling turned off?

Answer 7

SOCS has SH2 domain (is ubiquitin ligase)

Phosphatase also has SH2 domain

Question 8

What does a PTB domain in an adaptor protein recognise?

Answer 8

Recognises phosphorylated tyrosine residues (similar to SH2 domain but recognises 3 residues before the P-tyr)

Question 9

What does an SH3 domain recognise?

Answer 9

polyproline

Question 10

Where does the specificity of tyrosine kinase pathways come from?

Answer 10

The specificity of tyrosine kinase pathways comes from the adaptor proteins (eg SH2 domains etc) NOT from the kinase itself

Question 11

What are SH2 domains generally like?

Answer 11

Small and have their N and C termini close together at opposite sides of the binding site

Question 12

What is the adaptor protein for VEGF pathway?

Answer 12

Grb2

Question 13

What type of molecule is VEGF

Answer 13

VEGF is a dimer

Question 14

What type of receptor is VEGFR

Answer 14

Single pass receptor tyrosine kinase

Question 15

Briefly describe VEGF signaling pathway

Answer 15

VEGF binds VEGFR receptor monomers to bring them together.
Both monomers have intracellular low acting kinases.
Dimerization of monomers allows kinase domains to cross-phosphorylate.
Phosphorylated tyrosine residues on kinase domains of receptor are recognised by SH2 domain of Grb2
This reveals 2 SH3 domains on Grb2 which bind polyproline rich sequence in SOS protein bringing it to membrane

Question 16

What type of protein is SOS?

Answer 16

SOS is a GEF (for RAS)

Question 17

What does VEGF stand for?

Answer 17

Vascular endothelial growth factor

Question 18

What is the function of a GEF?

Answer 18

GEF = guanine exchange factor. Encourages dissociation of GDP from a GTPase and exchange with GTP

Question 19

What is the function of a GAP?

Answer 19

GTPase activating protein - encourages the hydrolysis of GTP - GDP in GTPases.

Question 20

What type of gene is the gene for RAS GTPase?

Answer 20

An oncogene - mutated RAS proteins are found in cancers (hydrolysis rate too slow and switch is left active for too long)

Question 21

How does RAS act as an effective switch?

Answer 21

When RAS binds GTP it forms a network of hydrogen bonds that fold two loops of the protein in towards GTP (switch 1 and switch 2). When GTP is hydrolysed these two switches spring out. This conformational change allows RAS to function as a switch.

Question 22

Which residue is commonly mutated in cancerous RAS proteins?

Answer 22

Gly12

Question 23

What is the RAS kinase cascade?

Answer 23

RAS - RAF - MEK - ERK

Question 24

What two states can ERK exist in?

Answer 24

ERK can either be transported out of Nucleus (via NES) or transported into nucleus (Via NLS)

Question 25

What affect does ERK have in the nucleus

Answer 25

ERK phosphorylates transcription factors in the nucleus (activating them)

Question 26

What will be transcribed if the RAS cascade causes a transcription factor to be phosphorylated and therefore bind the SERUM RESPONSE ELEMENT?

Answer 26

FOS

Question 27

What type of protein is FOS?

Answer 27

leucine zipper

Question 28

What is the function of FOS?

Answer 28

FOS binds JUN (diff leucine zipper) and create important TF AP1.

Question 29

How do FOS and JUN dimerise?

Answer 29

Dimerise through opposing charges, FOS has Glu residues which attract Lys residues on JUN

Question 30

What is the EGF released from the somatic gonadal anchor cell in worm vulval cell development?

Answer 30

LIN3

Question 31

What is the EGFR for 1prime cell fate specification in worm vulval cell development?

Answer 31

LET23

Question 32

What is the adaptor protein in the 1prime cell fate specification pathway in worm vulval cell development?

Answer 32

SEM-5

Question 33

What is the specific RAS protein which is activated by SOS in the 1 prime cell fate specification pathway in worm vulval cell development?

Answer 33

LET-60

Question 34

What is the transcription factor that is the target of the final kinase in the RAS signaling pathway in 1prime cell fate specification in worm vulval cell development?

Answer 34

LIN31