Lecture 16: Peroxisomes Flashcards
peroxisomes carry out a ____
variety of essential functions in a wide spectrum of organisms
peroxisome (descr.)
single membrane organelle that has fine granular matrix
peroxisomes are generally _____
spherical with diameters of 0.2 to 1 um
number and composition of peroxisomes _____
vary widely depending on physiological needs
peroxisomes are distributed _____
evenly in human cell
peroxisomes size depends on ____
diet of organism
peroxisomes under EM
electron dense surrounded by membrane
peroxisomes are organelles that ____
use molecular oxygen and hydrogen peroxide to carry out oxidative reactions
peroxisomes: 2 essential enzymes
-oxidase (produces H2O2)
-catalase (decomposes H2O2)
oxidase reaction
RH + O2 -> R + H2O2 (produces H2O2)
catalase reaction
decomposes H2O2
peroxisomes detoxify _____
several toxic molecules (ex. ethanol)
peroxidation (def.)
H2O2+ R’H2 —> R’+ 2H2O
site of lipid metabolism in mammalian cells
mitochondria & peroxisomes
site of B-oxidation of long chain fatty acids in mammalian cells
mitochondria & peroxisomes
site of bile synthesis in mammalian cells
mitochondria & peroxisomes
site of B-oxidation of long chain fatty acids in yeast cells
peroxisomes
peroxisomes are central to _______
lipid metabolism
Peroxisomes control ____
extent of oxidative stress with catalase by controlling levels of reactive oxygen species (ROS)
peroxisome function requires tethering to _____ (2)
lipid sources (lipid droplets)
lipid metabolizing organelles (mitochondria,ER)
lipid metabolizing organelles (2)
mitochondria
ER
size of peroxisome = how ____
metabolically active the cell is
2 types of disorders with peroxisomes
-protein deficiencies
-deficiencies in biogenesis of peroxisomes
peroxisomes disorders help to identify ____
human genes required for peroxisome function
class of inherited disorders that affect biogenesis of peroxisomes
Zellweger Spectrum Disorders
peroxisomes are required for proper ____
human development and physiology
peroxisomes function + neural defects
they catalyze 1st reaction in formation of plasmalogens (phospholipids in myelin)
defects in peroxisomes biogenesis -> neural defects
peroxisomes are the signaling platform for ____
antiviral response
immunity: increasing peroxisomes leads to ____ by ___
increased capacity of innate immunity
inhibiting RNA viral replication
Interferon (def.)
group of signaling proteins made and released by host cells in response to the presence of several viruses
-part of innate immunity
peroxisomes and interferon relationship
increase peroxisomes = increase activity of interferon simulated gene
interferon simulated gene (ISGs) (def.)
a gene that can be expressed in response to stimulation by interferon
Zellweger Spectrum Disorders (ZSS) and other peroxisomal diseases leads to the accumulation of _____
very long chain fatty acids in blood and many tissues
ZSS is the result from defects in at least of how many pex genes?
14
protein targeting to peroxisomes involves two pathways: _____
-direct import from cytoplasm
-import machinery of the ER
peroxisomes lack _____ and _____
genome
protein synthesis machinery
all peroxisomal protein are encoded in _____ and synthesized by ____
nucleus
ribosomes in cytosol
peroxisomes are completely dependent on ____ for biogenesis
completely dependent on import of protein for biogenesis
signal needed for the import of peroxisome matrix proteins
Peroxisome Targeting Signal (PTS)
two types of signals (PTS) for import of peroxisome matrix proteins
-PTS1
-PTS2
most common PTS signal
PTS1
PTS1 (descr.)
conserved C-terminal tripeptide sequence (SKL)
PTS1 is the primary _____
targeting signal used by majority of matrix proteins
PTS1 is ___ and ____ for targeting to peroxisomes (needed and enough for transport)
essential and sufficient
GTP with PTS1 motif is transported where?
peroxisomes
PTS2 (descr.)
conserved N-terminal nonapeptide (9 a.a.)
PTS2 sequence
(R/K)(L/V/I)(X5)(H/Q)(L/A)
PTS2 is used by ____
smaller subset of matrix proteins
characterization of pex targeting mutants is done with_____ because ____
yeast
B-oxidation of fatty acids only occurs in peroxisomes
characterization of pex targeting mutants method
*Mutagenize yeast cells in culture
*Divide in many aliquots
*Plate each aliquot on standard plate
*Replica plate
*Identify mutants that grow on complete medium, but fail to grow on plates with long chain fatty acids as sole carbon source
two proteins recognize proteins that have PTS1 or PTS2 bearing proteins
Pex5p
Pex7p
Pex5/7 ____ produces Pex5/7p (___)
gene
protein
Pex5p recognizes protein with _____ targeting signal
PTS1
Pex7p recognizes protein with _____ targeting signal
PTS2
recognition of PTS2 involves ____ and _____
Pex7p
factor X (varies from species to species)
recognition of PTS1 involves ____
Pex5p
Pex5p and Pex7p require ___
docking proteins/channels/translocation complex
Pex13p/Pex14p form complex exposed to ___
cytosolic surface of peroxisomal membrane
Pex13p/Pex14p are resistant to extraction with ___ so they are _____
-high pH carbonate buffers (still in pellet)
integral membrane proteins
peroxisome extraction: pellet
imbedded with membrane
peroxisome extraction: supernatant
inside the peroxisome
Pex14p binds to ___
both PTS receptors (Pex5p and Pex7p)
Pex14p is the docking site for both _____
Pex5p and Pex7p complexes
overall pex14p mechanism
pex14 binds and internalizes PTS receptors (like a channel) with the help of other membrane proteins
import of matrix proteins is ___ and doesn’t require ___ (not like ER)
post-translational
unfolding
matrix proteins are stabilized with ____ before import into peroxisome
disulfide bonds and chemical cross-linkers
size of several matrix proteins
> 450 kDa (ex. catalase)
9nm gold particles with PTS1 is where?
peroxisome
Pex5p/7p found in the matrix of peroxisomes suggest that ___
PTS receptors are co-imported with their substrates
Pex5 shuttling between cytosol and matrix steps
1) Pex5 forms complex with proteins with PTS1
2)Pex5 docks on peroxisomal membrane through Pex14
3)Part or all of complex translocated into peroxisomal matrix
4) Cargo released in matrix
5) Pex5p is mono-ubiquinated
6) Pex5p is de-unbiquinated and exported back to cytosol in ATP-dependent process
Pex5p is _____ and then ______ to be exported back in cytosol
mono-ubiquinated
de-ubiquinated
Different types of ubiquination have ___
drastically different function
polyubiquination leads to ____
protein degradation
import process of PTS receptors is poor understood but ____
Pex5 oligomer may act as a transient pore
polysome (def.)
group of ribosomes bound to an mRNA molecule like “beads” on a “thread
most integral membrane proteins of peroxisome are synthesized _____
on free polysome
integral membrane proteins are targeted and inserted _____
post-translationally into peroxisomal membrane
integral membrane proteins are targeted to peroxisome by various ____
membrane related PTS (mPTS)
mPTS have no ____
clear consensus sequence
hydrophobic trans-membrane segments of integral membrane proteins interact with ____
specific chaperone to prevent aggregation
integral membrane proteins and chaperone form ____ that is then _____
complex
targeted to receptor on peroxisomal membrane
PMP stands for ___
peroxisomal membrane proteins
chaperone/transporter for peroxisomal membrane proteins
pex19p
receptor for peroxisomal membrane proteins
pex3p
some organisms require an additional membrane protein receptor:
pex16p
PMP inserted into membrane through what mechanism?
unknown mechanism
Mature peroxisomes are generated by the uptake of ____
membrane and matrix proteins to distinct intermediates
peroxins (def.)
several protein families found in peroxisomes
peroxisome biogenesis method
1) early peroxins (ex. pex3p) are targeted to ER and translocated by Sec61p complex
2) peroxins are sorted to specific pre-peroxisomal domains within ER then exported into small vesicles/pre-peroxisomes
3)additional PMPs imported into pre-peroxisomes
4) additional matrix proteins imported to form peroxisomes
5) peroxisomes continue to grow by fission
1st peroxins that are used to make peroxisomes
pex3p - receptor for integral membrane protein
pre-peroxisomes also called___
ghosts
pre-peroxisomes become peroxisomes by the addition of ____ after ___
matrix proteins
integral proteins
organelle the contributes membranes for de novo peroxisome biogenesis
ER
Yeast: Peroxisomes originate from
modifying vesicular pathways at the ___
ER
Mammals: Peroxisomes originate from
combination of modifying vesicular pathways at the ____
ER and mitochondria
____ is a key factor for the formation of pre-peroxisomal vesicles
Pex3
lipid droplets are tethered to peroxisomes by tethering protein: ____
spastin
effect of lipid droplet tethering to peroxisomes on lipid metabolism (2)
1) decrease of the size of a lipid droplet over time
2) degradation of lipids from the droplet accelerates
spastin knockdown with RNAi result
reduced lipid transfer to peroxisomes
glycosome (def.)
variant of peroxisome
Trypanosoma brucei (the parasite that causes ____) compartmentalizes glycolysis in the _____
sleeping sickness
glycosome
Identification of divergent T. brucei Pex3 led to the discovery that _____
glycosome biogenesis is essential for parasite growth
