Intracellular Signalling - Protein Kinases

Question 1

What are the 3 main groups of protein kinases?

Answer 1

1. Serine/Threonine kinases
2. Tyrosine kinases
3. Dual-specificity kinases

Question 2

What is function of protein kinases?

Answer 2

Enzymes that facilitate the transfer of a phosphate group from ATP to a specific amino acid reside (Set, Thr or Tyr) on a specific protein

Question 3

What is result of phosphorylation of a protein?

Answer 3

Changes the function of the protein (may activate or inhibit)

Question 4

Where is the phosphate group from ATP added?

Answer 4

Onto the hydroxyl group (OH) on the side group of the amino acids

Question 5

What do serine/threonine kinases do?

Answer 5

Phosphorylate Ser and/or Thr residues

PKA, PKC, PKG

Question 6

What do tyrosine kinases do?

Answer 6

Phosphorylate only Tyr residues

Receptor TKs (insulin receptor)
Non-receptor TKs (Src)

Question 7

What do dual-specificity kinases do?

Answer 7

Phosphorylate Ser/Thr and Tyr residues

MAP kinase kinases

Question 8

What are phosphatases?

Answer 8

Remove phosphate groups from amino acid residues to oppose the effects of kinases

Question 9

What are the 2 major groups of phosphatases?

Answer 9

1. Ser/Thr-directed phosphoprotein phosphatases (PPPs)

2. Tyr-directed phosphotyrosine phosphatases (PTPs)

Question 10

Why are there not as many different phosphatases as kinases?

Answer 10

Due to the broad specificity of phosphatases

Question 11

How can kinases modulate protein function?

Answer 11

1. Phosphorylation of a protein leading to a conformational change that directly alters the function of that particular protein
2. Phosphorylation of a transcription factor that alters gene transcription and protein expression levels

Question 12

What occurs during MAP kinase cascades?

Answer 12

1. An MAP kinase kinase kinase (MAPKKK) phosphorylates and activates an MAP kinase kinase (MAPKK)
2. MAPKK phosphorylates and activates an MAP kinase (MAPK)
3. MAPK phosphorylates a downstream substrate (a phosphoprotein or eve another kinase)

Question 13

What are the 3 main MAP kinase cascades?

Answer 13

1. ERK pathway
2. p38 pathway
3. JRK pathway

Question 14

What is the ERK pathway activated by?

Answer 14

Growth factors and GPCR ligands

Question 15

What are the p38 and JRK pathways activated by?

Answer 15

Stresses and inflammatory cytokines

p38 and JRK sometimes known as the stress-activated protein kinases (SAP kinases)

Question 16

What is the NF-kB pathway activated by?

Answer 16

Mostly by pro-inflammatory molecules (interleukin-1 and TNF-alpha)

Question 17

What is ‘Gleevec’?

Answer 17

Protein kinase inhibitor - drug was initially developed to treat chronic myelogenous leukaemia (CML)

Question 18

How does Gleevec work?

Answer 18

Inhibits activity of the non-receptor tyrosine kinase BCR-Abl and the receptor tyrosine kinases c-KIT and PDGF Receptor A

Inhibits cancerous WBC proliferation

Question 19

In the NF-kB pathway, what are the receptors coupled to?

Answer 19

The activation of the MAP kinase kinase kinase MEKK3

Question 20

Describe NF-kB pathway

Answer 20

1. Receptors are coupled to the activation of the MAP kinase kinase kinase MEKK3
2. This phosphorylates IkB kinase (IKK)
3. This phosphorylates IkB (the inhibitory binding partner of NF-kB –> a transcription factor)

Question 21

What does phosphorylation of IkB result in?

Answer 21

Targets it to an intracellular protein degradation pathway (‘the proteasome’)

This frees NF-kB to translocate to the nucleus

Question 22

What is effect of free NF-kB in nucleus?

Answer 22

Acts as transcription factor to promote the transcription of inflammatory genes

Question 23

What is dysregulation of kinases linked to?

Answer 23

Cancer development

Question 24

How does phosphorylation differ to G-proteins?

Answer 24

In contrast to G-proteins (always switched on by GTP), phosphorylation may activate or inhibit protein function

Question 25

How are MAP kinases and glycogen synthase kinase (GSK)-3 affected by phosphorylation?

Answer 25

• MAP kinases –> activated by phosphorylation

- Glycogen synthase kinase (GSK)-3 –> inhibited by phosphorylation

Question 26

What do kinase cascades allow?

Answer 26

The signal to be amplified

Question 27

How do the MAP kinase cascades work?

Answer 27

1. A MAP kinase kinase kinase (MAPKKK) phosphorylates and activates a MAP kinase kinase (MAPKK)
2. In turn phosphorylates and activates a MAP kinase (MAPK)
3. Then phosphorylates a downstream substrate (a phosphoprotein or even another kinase).

Question 28

Describe effect when adrenaline binds to B1-AR

Answer 28

1. G protein is Gs
2. Stimulates adenyl cyclase
3. Stimulates cAMP
4. Activates protein kinase A
5. Activates phosphorylase kinase which continues the pathway for the breakdown of glycogen

Question 29

What is protein kinase A involved in?

Answer 29

‘fight or flight’ response in mammals

Question 30

Describe effect when ACh binds to Muscarinic M2

Answer 30

1. G protein is Gi
2. Inhibits adenyl cyclase
3. Reduces cAMP levels
4. Reduced activation of protein kinase A

Question 31

Describe effect when angiotensin II binds to AT1R

Answer 31

1. G protein is Gq
2. Activates phospholipase C
3. Produces DAG and IP3
4. DAG activates protein kinase C
5. IP3 increase Ca2+ which activates protein kinase C and Ca/CaM kinase

Question 32

Describe effect of neuropeptide or NO

Answer 32

1. Activates guanylate cyclase (no receptor/G protein)
2. Increases cGMP
3. Actives protein kinase G

Question 33

What is dysregulation of many kinases linked to?

Answer 33

Cancer development