Metabolism of parasites II Flashcards
Anaerobe Entemoeba hystolytica / Giardia intestinalis example
Organelle classification: mitosome: nothing happens inside the cell
Pyruvate - Fd- AcetylCoa- Acetate
1 NADP: carrier reduced, need to get rid of it
1 ATP also
What you do is: put 2 pyruvate: 2 NADPH generated: get 1 acetate/1 ethanol, problem solved: 1:1 ratio acetate/ethanol
In Giardia: hydrogen production but not inside cytosol (not hydrogenosome then)
One uses GDP other does not = metabolic paths are similar, just happens in different compartments
Giardia microaerophile example
Microaerophile: can multiply at very low o2 concentrations
no O2: final acceptor is hydrogen: fermentation
putting all electrons on Hydrogen = NAD are free= solves redox problem
high o2: it just dies, cant give anything to ferrodoxin, o2 catches everything
low o2: NADPH + H2 + O2 = NADP + 2H20 NADH oxidase diasphorase pathway: gets rid of the O2, gives all electrons to O2 too, no need to go ethanol
so it all goes acetate: grows a bit faster for a while, later switches back to ethanol when o2 is over
What happens if H2 production goes inside organelle?
Hydrogenosome! Trichomonas (also if no O2 usage anywhere)
Trichomonas vaginalis example (H2 inside organelle)
Hydrogen production is weird. 1e comes from pyruvate, other one is directly donated from malate: for some reason not the other electron is also loaded on something else: probably due to enzyme differences, leading to weird pathways
It’s using a free-floating complex 1, it just takes it and directly hands it over to H2
How to drug design for trichomonas? /Metranidazole + what happens in drug resistance?
eg. Metronidazole: gets electrons from Fd, technically good but its toxic to cells, you cant keep that.
Drug resistance? if you never use pyruvate inside the cell, and never use Fd: it cant take the electrons away from Fd
So go for another pathway in cytosol: generate ethanol!
Normally the ones who would have H2 would grow faster, because less ATP, but the ones that will keep ethanol now will survive
Why trypanosoma metabolism is weird?
- Excretes pyruvate for some reason
- bloodstream is not expressing much, tsetse fly expresses everything. Has acetate production, Krebs, succinate (fermentation)
- Trypanosoma organelle is a mitochondrion because it does everything
LECA: last eukaryote common ancestor anaerobic metabolism theory - how eukaryotes got anaerobic metabolism?
1) either all enzymes for it was there & inherited, and some lost it along the way
2) LECA did not have it, somehow evolved along the way
- then aerobes shouldn’t have any anaerobic genes
What is shown:
-anaerobic eukaryote and mammals have high similarity, they almost have the same enzymes / although no one really has the same organelle
eg. Krebs cycle very similar, uses RQ instead of UQ and they are also similar
-also there’s one organism that has all: Chlamydononas
has ferrodoxin in Chloroplast, Ethanol/Acetate metabolism, Formate
has cytosolic glycolysis + lactate ethanol fermantation
it even has classic oxphos in some stages
Everything is here. in different compartments
:SO LECA HAD IT ALL
So was hydrogen metabolism inside the organelle or outside originally (Giardia/Trichomonas/trypanosoma comparison)
Prolly inside, because in LECA probably everything was compartmentalized
Compartmentalization might be harder because enzymes are produced in ribosome inside cytoplasm = hard to move around
Now why trypanosome puts all of it back inside compartments, even glycolysis = hard to tell.
Summary of anaerobic metabolism in eukaryotes
All use similar enzymes/variation in electron acceptors/compartmentalization
But all are from organelle of mitochondrial origin = too similar
LECA had everything compartmentalized, at some point they moved back to cytosol
Trypanosoma brucei background
Extracellular pathogen, transmiitted by tsetse fly, causes african sleeping sickness
resistance occurs
60 mil ppl are at risk of infection
need to treat cattles to tackle it
should have been eradicated already: difficult because of tackles
WHO neglected disease: not much research
Bloodstream form T.brucei glycolysis***
O2 : glucose - 3C conversion in glycosome: 2 ATP lost
When there’s oxygen: in order to put 2 of the 3Cs through the pyruvate pathway, one of the 3Cs go and donate electrons on the oxygen on mitochondria, comes back and oxidized to same molecule, then it goes for pyruvate
It does this because in the pyruvate pathway you lose 1 NAD for each 3C, if you put both your 3Cs on the pyruvate pathway: redox cannot be done (only 1 NAD is obtained from 2nd 3C early pathway)
NET ATP: you lost 2 earlier, pyruvate pathway generates 1 ATP for each 3C: 0, then you get 1 more from pyruvate pathway outside the glycosome in cytosol: 2 ATP (1 for each C)
No O2: can’t put anything on O2: 1c follows pyruvate, other C follows glycerol pathway= 2 atp lost on early stages, 2 atp gained from 1 early glycerol pathway, 1 pyruvate pathway = inside glycosome: 1 from 1 pyruvate pathway
net: 1 ATP
doesn’t die immediately but survives like this for couple of hours
Role of glycosome + also evaluated with computer models
1) You can keep everything together/throw them out at the end of each lifecycle, rather than adjusting them 1 by 1, enzymes are very stable anyway cant get rid of them easily, cant reduce enzymes via growth either, growth slows when you transfer to tsetse fly
Solution: Trypanosome throws away the glycolysis enzymes! Glycosomes are very similar to peroxisomes anyway
2) Its a controlled environment: ADP stays/ATP stays=not used to get more glucose all the time, rather used for building block purposes
3) Is it an advantage for parasite:
We don’t know because we don’t know how they were before in evolution lol, what was before glycosomes
4) they thought if we get everything together glycolysis would be faster
=NOPE. they checked it, they separated everything, glycolysis is so fast that nothing really has time to get separated and not be found again xd
4) maybe it has a metabolic role? Turbo engine of glycolysis, dangerous glycolysis
eg. Trypanosomes: 1st part when you produce a lot of hexose from glucose might be really fast if you have enough glucose, and hexose might accumulate
Problem: T.brucei does not have the enzyme to check that, normally in humans if you have too much hexose it slows down
Solution: separate them w glycosome? Works-PC model shows. hexose does not accumulate.
Let’s test what happens once everything is in cytosol- wetlab: CKO the transfer chaperones of enzymes inside the glycosome (normally enzymes enter with chaperones)
And it was working: they tried it on soap: and all the glycosome enzymes were coming out early with the cytosol enzymes
It supported the PC model, indeed no hexose accumulation
You can use this as a drug therapy: just CKO the entrance of enzymes to glycosome: t.brucei will go crisis and die
-But :this one was not why glycolysis was moved to glycosome!
Bcs if you didn’t have this hexose inhibition before= no way you would survive
So you moved everything inside the glycosome, then brucei get rid of it thinking its useless, once you now put it back to cytosol it goes crisis = so it had it before
Study enzymes for drug targeting / enzyme kinetics
Supply = demand
X1 = constant, stable
Once you put too much glucose, intermediate production slows down = intermediate breakdown will become faster = to prevent intermediate accumulation
too much intermediate= accumulates, too less= no ATP, need balance on each side
How does enzyme kinetics work in glycolysis/rate of reaction depends on
1) amount of enzyme
2) concentration of substrates + ATP
3) conc. of the downstream product
if you don’t have enough ATP for eg. the enzymes that uses ATP will slow down, also depending on the downstream molecules
What can computer models do?
You can upload every enzyme kinetics result/the map = then it will make pyruvate as fast as the cells do
for eg. in Trypanosome, you remove 02: it makes glycerol
Measure how fast enzymes work depending on each condition
