Intracellular Signalling - Protein Kinases Flashcards
What are the 3 main groups of protein kinases?
- Serine/Threonine kinases
- Tyrosine kinases
- Dual-specificity kinases
What is function of protein kinases?
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
What is result of phosphorylation of a protein?
Changes the function of the protein (may activate or inhibit)
Where is the phosphate group from ATP added?
Onto the hydroxyl group (OH) on the side group of the amino acids
What do serine/threonine kinases do?
Phosphorylate Ser and/or Thr residues
PKA, PKC, PKG
What do tyrosine kinases do?
Phosphorylate only Tyr residues
Receptor TKs (insulin receptor) Non-receptor TKs (Src)
What do dual-specificity kinases do?
Phosphorylate Ser/Thr and Tyr residues
MAP kinase kinases
What are phosphatases?
Remove phosphate groups from amino acid residues to oppose the effects of kinases
What are the 2 major groups of phosphatases?
- Ser/Thr-directed phosphoprotein phosphatases (PPPs)
2. Tyr-directed phosphotyrosine phosphatases (PTPs)
Why are there not as many different phosphatases as kinases?
Due to the broad specificity of phosphatases
How can kinases modulate protein function?
- Phosphorylation of a protein leading to a conformational change that directly alters the function of that particular protein
- Phosphorylation of a transcription factor that alters gene transcription and protein expression levels
What occurs during MAP kinase cascades?
- An MAP kinase kinase kinase (MAPKKK) phosphorylates and activates an MAP kinase kinase (MAPKK)
- MAPKK phosphorylates and activates an MAP kinase (MAPK)
- MAPK phosphorylates a downstream substrate (a phosphoprotein or eve another kinase)
What are the 3 main MAP kinase cascades?
- ERK pathway
- p38 pathway
- JRK pathway
What is the ERK pathway activated by?
Growth factors and GPCR ligands
What are the p38 and JRK pathways activated by?
Stresses and inflammatory cytokines
p38 and JRK sometimes known as the stress-activated protein kinases (SAP kinases)
What is the NF-kB pathway activated by?
Mostly by pro-inflammatory molecules (interleukin-1 and TNF-alpha)
What is ‘Gleevec’?
Protein kinase inhibitor - drug was initially developed to treat chronic myelogenous leukaemia (CML)
How does Gleevec work?
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
In the NF-kB pathway, what are the receptors coupled to?
The activation of the MAP kinase kinase kinase MEKK3
Describe NF-kB pathway
- Receptors are coupled to the activation of the MAP kinase kinase kinase MEKK3
- This phosphorylates IkB kinase (IKK)
- This phosphorylates IkB (the inhibitory binding partner of NF-kB –> a transcription factor)
What does phosphorylation of IkB result in?
Targets it to an intracellular protein degradation pathway (‘the proteasome’)
This frees NF-kB to translocate to the nucleus
What is effect of free NF-kB in nucleus?
Acts as transcription factor to promote the transcription of inflammatory genes
What is dysregulation of kinases linked to?
Cancer development
How does phosphorylation differ to G-proteins?
In contrast to G-proteins (always switched on by GTP), phosphorylation may activate or inhibit protein function
How are MAP kinases and glycogen synthase kinase (GSK)-3 affected by phosphorylation?
- MAP kinases –> activated by phosphorylation
- Glycogen synthase kinase (GSK)-3 –> inhibited by phosphorylation
What do kinase cascades allow?
The signal to be amplified
How do the MAP kinase cascades work?
- A MAP kinase kinase kinase (MAPKKK) phosphorylates and activates a MAP kinase kinase (MAPKK)
- In turn phosphorylates and activates a MAP kinase (MAPK)
- Then phosphorylates a downstream substrate (a phosphoprotein or even another kinase).
Describe effect when adrenaline binds to B1-AR
- G protein is Gs
- Stimulates adenyl cyclase
- Stimulates cAMP
- Activates protein kinase A
- Activates phosphorylase kinase which continues the pathway for the breakdown of glycogen
What is protein kinase A involved in?
‘fight or flight’ response in mammals
Describe effect when ACh binds to Muscarinic M2
- G protein is Gi
- Inhibits adenyl cyclase
- Reduces cAMP levels
- Reduced activation of protein kinase A
Describe effect when angiotensin II binds to AT1R
- G protein is Gq
- Activates phospholipase C
- Produces DAG and IP3
- DAG activates protein kinase C
- IP3 increase Ca2+ which activates protein kinase C and Ca/CaM kinase
Describe effect of neuropeptide or NO
- Activates guanylate cyclase (no receptor/G protein)
- Increases cGMP
- Actives protein kinase G
What is dysregulation of many kinases linked to?
Cancer development
