Lecture 9: Trans-Golgi Network (TGN) Flashcards
TGN is the most ___
distal region of the golgi complex
TGN functions to modify and sort ____ from ____ and proteins & lipids from ____
newly synthesized proteins & lipids
-proximal golgi
-endocytic compartments
defects in sorting/release of cargo in TGN associated which diseases?
-autoimmune disease, cancer, neuropathology, diabetes
______ of viral proteins affect pathogenesis
TGN processing
major function of TGN
-sort proteins (localization) but also modifies proteins
TGN is _____ & _____distinct from golgi stack
-morphologically & biochemically
morphological differences between TGN and golgi stack
-tubular network and associated vesicles
-cisternae are not flattened against golgi stack
-cisternae has peeled away from trans cisternae of golgi stack
biochemical differences between TGN and golgi stack
-osmium reduced by unsaturated lipids in cis-golgi (reducing environment)
-TGN has acid phosphatase (acidic environment)
TGN is considered _____ by many reasearchers
separate entity
evidence that TGN is separate
-TGN reacts differently to drugs and temperatures that impair protein/membrane trafficking
BFA (Brefeldin A) causes ___ (for golgi stack +TGN)
-TGN fuses with endosomal membranes
-Golgi stack fuses with ER
Membrane an protein cargo blocked in TGN and ER at which temperatures?
-TGN: 20 C
-ERGIC: 15 C
Enzymes of TGN do what?
-terminal glycosylation
-sulfation
-endoproteolysis
TGN: terminal glycosylation (def.) + why?
-addition of sialic acid to N-linked oligosaccharides by dialytransferase (ST)
-keeps negative charge on cell surface
-keeps water at cell surface
TGN: sulfation (def.)
-addition of sulfate groups to Tyrosine
-can affect protein-protein interactions
human brain is rich in ____
sialic acid (4X) for neurotransmission + memory
loss of tyrosine sulfation can affect ___
blood clotting (VIII)
Furin is ___
a transmembrrane protein in TGN that cleaves pro-proteins
Furin cleaves where?
R-X-(R/X)-R
Furin + COVID-19
-furin cleavage of spike protein promote intereaction of virus particles with receptor ACE2 by exposing receptor binding domain (RBD)
presence of cleavage site associated with _____
highly pathogenic influenza virus strains
furin cleaves what?
mammalian, viral, bacterial substrates
furin inhibitors are good antivirals but there is a problem: ____
-furin does many important function in mammals but viruses take advantage of it
TGN is a _____ site for proteins/lipids in eukaryotic cells
major sorting site
3 main sorting pathways of TGN +examples + signal needed?
-to endosomes (ex. lysosomal enzymes) + signal needed
-to secretory granules (ex. regulated secretion) + signal needed
-constitutive transport to PM + no signal needed (except in polarized cells)
Alzheimer disease (AD) is caused by ___ due to
accumulation of plaque that contain AB oligomers due to abnormal cleavage of amyloid precursor protein by B-secretase (makes AB oligomers)
Production of AB oligomers happens in ___ because ____
-TGN
-b-secretase which are normally localized in endosomes but decrease in GGA or increase in retromer make B-secretase localize in TGN
AB plaques make by ___ (2)
-B-secretase
-gamma-secretase
If movement of beta-secretase to TGN ___ or b-secretase to endosome is ____, cleavage of APP increases
-increases
-blocked
normal cleavage of APP is by ___
a-secretase
live cell imaging allows for ____
visualization of cargo and interaction with membrane compartments and cytoskeleton
temperature blocks are useful for ___
synchronizing cargo flow
temperature block of TGN
20 C
coat protein for constitutive transport from TGN
-no known coat protein
carriers size for constitutive transport
-large structure (170 -1700nm) (half size of cisternia)
-variable size
shape of carriers for constitutive transport
constitutive transport is ____sensitive and regulated by ___
-BFA
-ARFs (small GTPases)
constitutive transport requires ___motores (____), ____and ___
-molecular motors
-kinases
-rabs
kinesin help with the movement of ____
carriers
constitutive transport to PM: sorting signals ___
not needed (default pathway)
VSG is a ___ targeted protein
basolaterally
post TGN cargo (constitive transport) travels along ____
microtubules
for polarized cells, ____ are needed for transport to apical/basolateral membranes
different signals
TGN structure is key to ____
its sorting ability
TGN is organized into ____
subdomains of different proteins & lipids
TGN enriched in _____ which serves as _____
-PI4P
-binding platrom for proeins involved in cargo sorting + vesciel formation
organization of TGN subdomains dependent on ____
Rab GTPases
TGN domains that sort cargo to different places have ___
different residues
sorting of proteins in TGN real time method
live-cell imaging
temperature block permits _____
synchronization of traffic moving through TGN
GPI protein targeted to _____
apical surface
adenoviruses are good for studying ____`
cargo targeting from the TGN
Fluorescence microscopy helps use determine ____
when cargo is sorted and transport routes and which compartments are involved
Post-golgi carriers _____ with endosomes
-don’t intersect
regulated secretion are in response to ___
-signal (hormone/neurotransmitter)
subset of secretory proteins (inslunin neurotransmittes) are ___ in
concentrated (200-400x) and stored in specialized from mature granules
mature granules are from ___
maturation of immature secretory (ISGs)
contents of MSG secreted in response to _____
extracellular simulates (ex. neurotransmitter)
MSG has ____ (desc.)
dense core that contains high conc of protein
proteins aggerate in response to ___ and ___ invitro
low pH and Ca++
pH of TGN is ____ than golgi stack and has more ____
-lower
-Ca++
when regulated secretory protein is expressed in cell that doesn’t normally express it, ______
protein enters regulated secretory protein suggesting that protein contain inherent targeting signals
selection of regulatory secretory pathway: sorting by entry
-proteins destined for SG aggregate in special regions of TGN (high Ca++ and low PH (6.5)
-may/may not be signal mediated
-confirmation-dependent signal binds to receptor to TGN –> individual proteins/aggregates into ISGS
selection of regulatory secretory pathway: sorting by retention
-non-regulatory secretory proteins removed by CCVs (clathrin coated vesicles)
-removal results in maturation into MSGs
clathrin coats on ISG & TGN: selection method
selection by entry and selection by retention
clathrin coats on ISG OR TGN: selection method
only one selection method is right
TGN: entry
ISG: retention
antibodies that recognize either forms of proinsulin/insulin can be used ___
to determine where processing of regulated secretory protein occurs in membrane compartments
Immuno-electron microscopy (def.)
gold particles coated in protein A used to detect antibody bound protein by transmission electron microcopy
Cpn60 localizes in _____
secretory granules in pancreatic cells
TM shows that proinsulin processing ____
happens after it leaves TGN and granules mature
