PSC2002/L23 PK and Protein Phosphatases Flashcards
What can activate protein kinases? (3)
cGMP (PKG)
Increase in Ca2+
PKB & protein tyrosine kinases (only phosphorylate serine residues)
What is the key difference between the cGMP and cAMP signalling pathways?
GPCRs not involved in cGMP pathway
What are the 2 distinct types of GCs?
Soluble form (sGC) activated by NO
Plasma membrane bound (pGC) activated by peptide agonists
Give another abbreviation of PKG.
cGK
What is the role of cGMP in the cGMP pathway?
Activates PKG
PKG phosphorylates serine/threonine residues
What breaks down cGMP?
cGMP-dependent PDEs
How can nitric oxide production be stimulated?
Increasing calcium
How permeable are endothelial cells to NO?
Very permeable
Where is ANP released from?
Atrial cells
How can a singular peptide increase cGMP? (3)
Binds to plasma membrane
Covalent change in guanylyl cyclase
Leads to increase in catalytic subunits which make cGMP
Where is NO released from?
Endothelial cells
What is the effect of NO in VSM?
Activates sGC/cGMP
Vasodilation and BP decrease
What kind of drugs are used to treat angina?
NO generating drugs
What kind of drug is Viagra (sildenafil)?
Type 5 cGMP PDE inhibitor
What is the effect of viagra (sildenafil)? What is it used to treat? (2)
Rise in cGMP relaxes SM in some tissues
Used to treat erection problems and pulmonary hypertension
Describe the effect of heat stable enterotoxin from E. coli in the intestine. (3)
Activates pGC/cGMP
PKG phosphorylates & activates CFTR
Leads to secretory diarrhoea
Describe the LPS (endotoxin) from Gram -ve bacteria. (3)
Increases iNOS (inducible NO synthase) expression
Excessive NO production
Can lead to clinical shock due to severe BP drop
How many different isoforms and groups of PKC are there?
11 isoforms
3 groups - conventional, novel and atypical
What is required for PKC to become active?
Phospholipid binding
What keeps PKC inactive? (2)
R domain has a pseudosubstrate motif
Keeps kinase inactive by occupying substrate binding site on C4 domain
Describe the activation cycle for cPKC (following a rise in cytosolic Ca2+). (3)
Ca2+ binds to C2 domain
PKC translocates to PM to bind DAG via C1 domain
PS motif disengages from C4 domain, allowing substrates to bind and be phosphorylated
How can cPKC be artificially activated? (2)
Phorbol esters (plant alkaloids which are tumorigenic)
Directly bind to PKC
What are the 2 main types of Ca2+/Calmodulin-dependent Protein Kinases?
Those with narrow substrate specificities (e.g., phosphorylase kinase only phosphorylates ‘phosphorylase’
Those with broad substrate specificities (e.g., Multifunctional CaM kinase II (CaMKII) which phosphorylates many substrates)
Give 3 functions of CaMKII.
- Regulates N-methyl-D-aspartate (NMDA) receptors by phosphorylating sites on NR2A and NR2B subunits
- Enhances InsP3 formation by inhibiting inositol phosphorylate 5-phosphatase
- Central role in frequency decoding of calcium signals and acting as molecular switch in learning and memory
- Phosphorylates PLB to control SERCA2 pump - works in synergy with PKA to inhibit PLB effect on SERCA
What is the function of protein phosphatases (PP)?
Remove phosphate groups from phosphorylated proteins (Ser/Thr & Tyr residues)
What are the 4 major classes of Ser/Thr PPs?
1, 2A, 2B, 2C
1, 2A, 2C show broad & overlapping substrate specificity
“B (calcineurin- CaN) has more restricted specificity & requires Ca2+/CaM activity
How are PPs regulated?
By inhibitory proteins type 1 and 2
Give an additional class of PPs.
Tyrosine PPs, in membrane bound and cytosolic forms
Give 2 chemical inhibitors of protein phosphatases and what they block.
Okadaic acid (OA) blocks PP1 and PP2A
Cyclosporin A very specific for calcineurin (PP2B) used clinically for immunosuppression via effects on T-cells
Where does okadaic acid originate from?
Dinoflagellates (algae) produce this toxin
Accumulates in marine sponges and shellfish
When ingested causes diarrhetic shellfish poisoning (DSP)
How does diarrhetic shellfish poisoning (caused by okadaic acid) cause acute diarrhoea?
Increased paracellular permeability
More active CFTR, promoting fluid loss from GI tract
How does PKA lead to glycolysis? (3)
Switch on PKA through GPCR
Phosphorylates PK to A form
Glycogen breakdown
What is the role of PKA with regards to PP inhibitory proteins?
Activate PP ‘inhibitory’ proteins
Inhibitory proteins bind to and inhibit PPs during glycogen breakdown
Rise in [cAMP] favours glycogen breakdown
Describe the synergy between cAMP and Ca2+ in skeletal muscle. (2)
Link between depolarisation and opening of Ca2+ stores
Ca2+ feeds into PK helping it to work better
What are the requirements of PK to work in skeletal muscle?
PKA phosphorylation and Ca2+ binding
What are the subunits of PK?
a, B, d, Y
PKA phosphorylation of a and B subunits increases calcium sensitivity of PK
Which 2 signalling pathways interact to regulate insulin secretion from beta cells?
cAMP signalling and tyrosine kinase signalling pathways
