2.9: Signaling via Protein Modifications

Question 1

state and describe the two mechanisms of signaling via enzyme coupled receptors

Answer 1

1. phosphorylation: signal perception triggers activation of receptor kinases or receptor associated kinases
2. proteolysis: signal perception triggers protein cleavage or degradation

Question 2

state the 3 examples of phosphorylation

Answer 2

1. receptor tyrosine kinases
2. tyrosine kinase associated receptors
3. receptor serine/threonine kinases

Question 3

describe the common structure of receptor protein kinases (RTKs) and their functions

Answer 3

• different ec domains bind different ligands
• has tm domain
• ic tyrosine kinase domain phosphorylate different targets at tyrosine residues

Question 4

how are RTKs activated

Answer 4

1. ligand binding (signal)
2. transautophosphorylation
   (trans = on diff RTK molecule, auto = RTKs can act as RTK)

Question 5

state the structure of activated RTKs

Answer 5

dimers

Question 6

t/f after signal proteins bind to RTKs, the transautophosphorylation must activate each others kinase domains are the same time

Answer 6

true

Question 7

t/f the signal protein for RTKs don’t always have to be dimers

Answer 7

yes

Question 8

RTK transautophosphorylation can recruit other signaling molecules, this means the acitvated RTK can act as what type of protein

Answer 8

scaffold protein

Question 9

when rtks act as a scaffold, what do proteins bind to

Answer 9

phosphorylated tyrosine

Question 10

which domains can signaling proteins bind to RTKs to

Answer 10

SH2 or PTB domains

Question 11

explain how signaling proteins can bind to RTKs via SH2 or PTB domains

Answer 11

each SH2 domain has two binding sites for specificity: recognizes the phosphorylated tyrosine, recognizes nearby amino acids
these ensure that SH2 domains bind to specific phosphorylated proteins

Question 12

t/f activated RTKs can recruit other signaling molecules and often activates Ras-GEFs

Answer 12

true

Question 13

Ras family proteins are related to other monomeric ________

Answer 13

GTPases

Question 14

Many RTKs signal to activate _____ monomeric GTPases

Answer 14

Ras

Question 15

what are MAP kinase

Answer 15

mitogen activated protein kinase - signal that generates mitosis

Question 16

do all MAP kinases activate mitosis

Answer 16

no

Question 17

which cascade can activated ras activate

Answer 17

MAP kinase cascades

Question 18

what can MAP kinases convert a short term RTK activation at the cell surface into

Answer 18

a stable/long term change in gene expression

Question 19

which type of feedback do MAP kinases provide

Answer 19

negative feedback

Question 20

How many of each of the following do humans have: MAPKKK (Raf), MAPKK (Mek), MAPK (Erk)

Answer 20

MAPKKK: ~7
MAPKK: 7
MAPK: 12

Question 21

state what type of changes the effector proteins cause at the end of the MPA kinase cascade

Answer 21

• changes in protein activity (protein x, protein y)
• changes in gene expression (transcription reg prot A and B)

Question 22

state what can provide specificity to MAP kinase cascades

Answer 22

scaffold proteins

Question 23

drosophila sevenless signaling is an example of what

Answer 23

RTK signaling

Question 24

Drosophila compound eyes are made of ___________
Each ommatidia has _ photoreceptor cells (R1-R_)
The R_ cells is required to detect UV light

Answer 24

ommatidia, 8, 7

Question 25

which is the first cell to differentiate in the ommatidia (R what) and which is last

Answer 25

R8, R7

Question 26

in sevenless signaling: RTK = _________ Ligand = _________ Adaptor protein = _________ Ras-GEF = _________

Answer 26

RTK = Sevenless (Sev) * Ligand = Bride of Sevenless (Boss) * Adaptor protein = Grb2 (Drk) * Ras-GEF = Son of Sevenless (Sos)

Question 27

what is the end product of the sevenless signaling pathway

Answer 27

differentiation into R7

Question 28

describe how RTKs can signal through phosphoinositides (PIPs)

Answer 28

1. RTK activated by a survival factor 2. RTK activates PI 3-kinase 3. PI 3-kinase converts PI(4,5)P2 to PI(3,4,5)P3 4. PDK1 & Akt bind PI(3,4,5)P3 5. PDK & mTORC2 phosphorylate Akt 6. Akt phosphorylates Bad to release Bcl2 to inhibit apoptosis (in order to survive = can't die)

Question 29

there can be cross talk between ?

Answer 29

RTK and GPCR signaling

Question 30

what type of receptors have no kinase activity

Answer 30

cytokine receptors (no tyrosine kinase domain)

Question 31

those receptors that have no kinase activity, they associate with what to be able to signal

Answer 31

cytoplasmic tyrosine kinase

Question 32

which mechanisms remain similar between tyrosine kinase associated receptors and RTKs

Answer 32

transautophosphorylation and protein binding to the phosphorylated receptor

Question 33

compare and contrast between receptor serine/threonine kinases and RTKs

Answer 33

Similar to RTKs: * Extracellular ligand binding domain * Transmembrane domain * Intracellular kinase domain * Multiple receptors associate in response to signals But: kinase domains phosphorylate serine and/or threonine residues in targets

Question 34

delta notch is an example of what type of signaling and notch signaling involves signaling via (2)

Answer 34

- contact dependent signaling 1. endocytosis 2. proteolysis

Question 35

1. where in the cell are notch proteins made and why 2. where is notch cleaved into two pieces

Answer 35

1. in the ER bc TM 2. golgi

Question 36

state the signifier of proper notch

Answer 36

the cleavage

Question 37

do the cleaved pieces of notch stay together or go apart when they move to the plasma membrane

Answer 37

stay together

Question 38

interaction with delta results in further/less notch proteolysis

Answer 38

further

Question 39

the ______ part of notch directly interacts with delta on the surface of the other cell, delta notch is _______ into the delta expressing cell for proper gene expression and the remainder of notch is cleaved at ____ more sites

Answer 39

extracellular, endocytosed, two

Question 40

after delta-notch is endocytosed into the delta expressing cell, the remainder of notch is cleaved at how many more sites

Answer 40

two

Question 41

does the cytosolic head or tail of notch move to the nucleus and what does it promote

Answer 41

tail, the notch tail promotes transcription of notch target genes

Question 42

if there is transcription of notch target genes, is delta activated or repressed in this cell

Answer 42

repressed - but you might have some if the proteins made were repressors

Question 43

does the cell with active notch target genes differentiate or not differentiate

Answer 43

not differentiate

Question 44

how do notch small fragments free up in the ec space

Answer 44

through cleavage

Question 45

state the 4 types of mechanisms that hedgehog signaling combines

Answer 45

1. GPCRs, cAMP, PKA 2. proteolysis 3. cytoskeleton - mediated transport 4. paracrine signaling

Question 46

describe the actions when hedgehog signaling is present

Answer 46

1. Hedgehog binds and inactivates Patched 2. Smoothened is active and moves to the tip of the primary cilium 3. Gpr161 and PKA are inactive 4. Gil3 is not proteolytically processed so it does not inhibit hedgehog target genes 5. SuFu and Gli2 move along microtubules to the tip of the primary cilium 6. Smoothened releases Gli2 from SuFu 7. Gli2 moves along microtubules from primary cilium to nucleus 8. Gli2 activates hedgehog target genes

Question 47

describe the sequence of events when there is no hedgehog signal

Answer 47

1. Patched is active in the cilium 2. Active Patched inhibits Smoothened and keeps Smoothened out of the primary cilium 3. SuFu binds and inhibits Gli2 & Gli3 4. GPCR (Gpr161) is active 5. Active Gpr161 promotes cAMP synthesis 6. cAMP activates PKA 7. PKA phosphorylates Gli3 8. Gli3 phosphorylation causes Gli3 proteolytic processing 9. The remaining fragment of Gli3 moves to the nucleus to repress expression of hedgehog target genes

Question 48

what processes are the following involved in 1. notch (3) 2. hedgehog (Shh) (5)

Answer 48

1. tissue patterning, neurogenesis, stem cell renewal 2. neural tube closure, tissue patterning, limb development, lung development, stem cell renewal

Question 49

Which of the following terms best describes Sevenless signaling? a) Contact dependent signaling b) Paracrine signaling c) Two-component signaling d) Receptor threonine/serine kinase signaling

Answer 49

A