Week 6 Flashcards
What can ROS also function as
Essential physiological regulators
What happens if ROS is high
Phagocytes has vital antimicrobial functions can also have deleterious effects on the host tissue injury and hyper-inflammatory response
What happens if ROS is low
NOX1 activated in epithelia cells affecting the cellular redox status and physiologically important cell proliferation differentation and motility
How is the redox regulation by ROS modulated
Specific reactive cysteine reisude within redox sensitive target protiens
What leads to the reversible modification of enzymatic activity
Oxidation of thiol groups SH of the cysteines
What is the first step of cysteine biochemistry
Formation of intra molecular and intermolecular disulfide bonds.
How are disulfide bonds formed
When two adjacent thiol groups are oxidized releasing proton and electron to form a covalent disulfide bond they can also be formed when reactive sulfenic acid interacts with nearby cysteines
What is the steps of oxidation of reactive thiol groups
Start with the thiol group move to the sulfenic form then fulfinic form and then finally sulfonic form which is not reversible
What is Glutahinoylation
A post translational protein modification it is a binding of glutathione tripeptide to a via the formation of a disulfide bond with a protien thiol
What can ROS regulate with critical singaling molecules
Cell proliferation, survival differenitation and metabolism
What do these critical signaling moelcules contain
Redox-reactive cysteine residues
What is there also potentinal for
DNA damage Iron homeostasis and Anti-oxidant and anti inflamatory repsonse
What is the key molecules of the redox regulation
Transcription factors Nrf2 and enzymes that control the thiol-disulfide exchange and levels of ROS (peroxiredoxin,thiroedoxin and sulfiredoxin)
What does Keap1 serve as and why
Oxidative stress sensor and it is a cysteine-rich protein and when modifications of thiol groups in this protein induce significant conformational changes and interactions with other proteins
What happens to Nrf2 in unstressed conditions
Nrf2 is associated with the Keap1 dimer and will undergo constans ubiquitination by Cul3 so Nrf2 is short lived
What hapens to Nrf2 under oxidative stress conditions
ROS will induce oxidation/chemical modifications of the cysteine reisudes which inactive Keap1 Nrf2 translocates to the nucleus and heterodimerizes with sMaf and now will bind to the antioxidant response elements that will now induce the expression of genes encoding antioxidant enzymes and cytoprotective protiens
What can Nrf2 do
Antioxiant enzymes are upregulation of genes encoding the enzymes that control thiol/disulfide and the intracellular leves of ROS
What are Peroxiredoxins
Reduce and inactivate hydrogen peroxide and organix peroxides and are small protiens and present in all biological kingsoms
What do Prxs usually contain
Two cysteine residues
What are the difference between the two cysteine residues
One is specifically oxidizes by hydrogen peroxide to cysteine sulfenic acid and this is called peroxidatic Cp the other cysteine is involved in the formation of a disulfide linkage with CP and is called the resolving Cys CR
Do all peroxiredoxins contain Cr
NO
What do Prxs function as
Homodimers arangend in a head to tail orientation from Cp and Cr cysteines
How many members are in the human family of perociredoxins
6
What are the three subfamiles of prx enzymes
Typical 2 cys
Atypical 2-cys
1-cys
What occurs in the Typical 2-cysteine peroxiredoxins
contains both Cp and Cr resudues
What happens to Typical 2-cys if H202 is present
Oxidizes the thiol group of CP to form the sulfenic acid intermediate this will then recat with the Cr forming an intermolecular disulfide bond 2 H202 can be used to generate two disulfide bonds
How do Typical 2 cys reverse back
Trx is needed to act as a biological reducing agent
What happens when Prxs recat with additional H202
They can become hyperoxidized to cysteine sulfinc acit before the disulfide bonds can form what can cause inactivation of peroxidase activity and protien aggregation
What can fix herpoxidized Prxs
Sulfiredoxin Srx reducing the sulfinic group in an ATP-dependent recation
What is the different between Typical 2-cys and Atypical 2-cys
Atypical forms intramolecular disulfide linkage
What is different abotu 1-cys
Contains only one cysteine residue Cp so no disulfide bond is made
How is 1-cys regenerated
It can be reduced by glutathione GSH cataylzyed glutathione S-transferase not by thioredoxin
What are the two enzymes the thioredoxin system consists of
Thioredoxin and thioredoxin reducates and NADPH
How do thioredoxin catalyzing the reduction of other proteins
Thiol-disulfide exhange disulfide bond into two Sh groups
What is the pathway of the Thioredoxin system
Thioredoxin reducates is a selenoenzyme which gets reduced by NADPH and then reduces the disulfide bond
What is the electron transfer process
NADPH–> TrxR –> Trx so you have a reduced level of thioredoxin which will catalyze disulfide bond in many protien such as peroxiredoxins
Why else might cells produce hydrogen peroxide
Purpose of intracellular signaling in response to stimulation through various cell surface receptors required for propagation of growth factor singaling
What are growth factors give examples
PDGF and EGF
How do growth factors work
Activate PTKS which then phosphorylation of effector proteins and the steady state level of PTP
What do PTPS do
Remove phosphate groups from a protien
How are PTP blocked
PTP can be induced by hydrogen peroxide which is produced by the NOX enzymatic complexems
What does blocking PTP also do
Assembly of various signaling protiens like PTKS and Src family which is phosphorylated by PTKs in response to growth factors which then results in NoX activation and Src activation (inhibiting perociredoxin)
Why is peroxiredoxin need to be inhibited by Src
To avoid hydrogen peroxide degradation so that in can inhibit PTP and activate Src kinase
What protiens are produced in H202
Wound healing and tissue regenration
What is a redox pair
One acts as an electron donor and one as an electron acceptor
What are examples of redox pairs
NAD+/NADH
NADP+/NADPH
GssG/2GSH
Cys/CYSSCy
AA/DHAA
What is the key molecules of redox regulation
GSH/GSSG
What is the ratio of GSH.GSSG
High and varry intracellular levels is 3-10mM and the ratio is 100/1 GSH 2-10 uM GSH 5/1 (lower antioxidant capacity)
What can the redox state be characterized by
Redox potentional using the nernst equation
What is the Nernst equation
E= -E0 - (2.3RT/zF)log(red/ox)
What is the equation for GSH
It needs to be squared because two GSH molecules to form one GSSG moelcuels
In the case of glutathione was does the redox potential depend on
The ration and the GSH concnetration
In different parts of the cell what is the redox potentinal
Negative so the homeostatic redox balance is shifted to reduced molecules reduced molecules is higher than oxidized molecules
What is the most reduced microenvinronment
Mitochondria than the nuclees then the cytoplasm followed by the extracellular space
What is microenvinronment oxidized in association with
Proliferation to differentation growth arrest and apoptosis
What does redox potentinal of tissues depend on
GSH/GSSG and cysteine and cystine
What did the study show
Wide distribution of human blood plasma redox potential GSH/GSSG and Cys/CysSScys there was a linear increase of cysteine/cystine redox potential with age which indiccates age dependent oxisation of cysteine in blood
What was the results
Continous linear increase in oxidative events the capacity of GSH is mainitained until 40-50 then declines rapdily
What would you see in people not taking antioxidants, smokers dirnker and indviduals with dieases
A higher redox potentinal
What could be an assement of oxidative stress anc predictive markers of health
GSH/GSSG and Cys/Cyss but need to take into account other redox couples
