Redox signalling Flashcards
1
Q
radicals (ROS)
A
- A molecule with a single unpaired electron • Nitric oxide (not ROS but radical gas) • Superoxide • Hydroxyl radical • Hydrogen peroxide • Lipid peroxyl radical
2
Q
production of ROS
A
- Mitochondria –> oxidative phosphorylation can leak electrons at certain electron chain complexes which produces superoxide anions
- Cytosolic Fe2+ and H2O2 –> Fenton reaction produces hydroxyl radicals
- ER –> misfolding of proteins can lead to ER stress and ROS production
- Peroxisomes –> B-oxidation of LCFA (fatty acids) produces ROS
- Oxidases like NADHP oxidases produce ROS
- CYP450 (phase 1 enzymes) produce ROS when detoxifying molecules
- NO synthase –> produces NO which is a radical and can form ROS when interacting with other molecules/radicals
3
Q
ROS and RNS damage
A
- DNA damage –> 8-oxoguanine
- Protein damage –> protein carbonyl groups
- Lipid damage –> malondialdehyde and 4hydroxynonetal
4
Q
DNA damage - ROS
A
- More than 25 possible lesions
• Deamination: C –> U repaired by BER
• 8-Oxoguanine –> altered G repaired by BER
• Single strand breaks repaired by HR or NHEJ
5
Q
Nitric oxide - function and general info
A
- Free radical gas
- First identified as endothelial derived releasing factor
- Lipid soluble
- Short lived (4-6sec)
- Low conc –> signalling in circulatory and nervous system
- High conc –> immune response signalling
- Nitrosylation –> post-translational modificcation using NO
- Smooth muscle relaxation
6
Q
NO synthesis
A
- Precursor: L-arginine
- Reaction is catalysed by nitric oxide synthases (NOS)
- Three types of NOS depending on cell type:
• NOS 1 (nNOS)
Neuronal cells (CNS and PNS) and platelets
Calcium dependent
Neuronal communication
Constitutively expressed (always at same level)
• NOS II (iNOS)
Most nucleated cells mainly macrophages
Inducible expression
Involved in inflammatory response
• NOS III (eNOS) Endothelium and neural cells Calcium dependent Regulation of the vasculature - NO can form ROS or RNOS radicals that will damage your cells adverse effects of NO
7
Q
NADPH oxidases
A
- NADPH oxidases catalyse the formation of superoxide by transferring one electron to oxygen from NADPH
- The superoxide is then dismutated to H2O2 which partakes in redox signalling by altering redox sensitive proteins
8
Q
antioxidant systems
A
- Non enzymatic
• Vitamin C and E
• In food
- Enzymatic
• Glutathione transferases
Dimers
Phase 2 biotransformation --> Couples gluthione to a phase 1 metabolite
• SOD: Superoxide --> hydrogen peroxide
CuZnSOD
MnSOD
EcSID (extracellular)
• NADPH quinone oxidoreductase
9
Q
NRF2 - function
A
- NRF2 co-ordinately activates cytoprotective genes
• Is a oxidative stress sensor - Induces glutathione synthesis, antioxidant expression, detoxyfication of xenobiotics and drug transport
- Master regulator of AOX system: metalbinding proteins, gluthatione proteins, NADPH prouction, quinone detox proteins, etc.
10
Q
NFR2 - production
A
- NRF2 is normally steadily produced and degraded via UPS
- After stress NRF2 is phosphorylated by kinases and keap1 which is part of the ubiquitination complex is damaged by the stressor (ROS) meaning that NRF2 is not degraded
11
Q
oxadative stress and cancer
A
- ROS uprgulates many hallmarks of cancer: H2O2 activates: 1. PI3K --> growth 2. HIF --> angiogenesis and metabolism 3. NFkB --> inflammation and survival 4. MAPKs --> proliferation
- At some point the higher the ROS gets the less beneficial it gets for cancer since there will be too much DNA damage and the cell dies
12
Q
protein folding
A
- Disulphide bridge formation requires transfer of electrons –> ROS and thus redox
- PDIs can take electrons - be reduced - from proteins (from the SH) so they form S-bridges
- PDIs need to be oxidised back so they can fold more proteins –> oxygen is last acceptor
- In hypoxic environment porteins will misfold because all PDIs are reduced and ER stress occurs –> ATF4 activation increases OAX, autophagy and apoptosis to prevent further protein misfolding and DNA damage
