Protein trafficking Flashcards
(77 cards)
1
Q
how do proteins get to a location?
A
sorting signal
if no sorting signal then stays in cytosol
2
Q
how do proteins get to a location?
A
sorting signal
if no sorting signal then stays in cytosol
3
Q
types of sorting signal?
A
patch- AAs make patch in 3d form
sequence- AAs at the end of a chain
4
Q
what type of sequence codes for nuclear import?
A
K/R rich
5
Q
what type of sequence codes for mitochondrial import
A
Amphipathic/ alpha helix
6
Q
what type of sequence codes for ER import
A
hydrophobic AAs
7
Q
what size protein can fit through the nuclear pore
A
8
Q
where can a signalling sequence be recognised
A
membrane bound receptor or soluble receptor
9
Q
where do proteins get synthesised
A
in cytosol ( ribosomes)
10
Q
how do proteins know to go to the nucleus
A
nuclear localisation signal
11
Q
what makes up the nuclear pore complex
A
nucleoporin proteins in a basket arrangement
12
Q
what size proteins can fit through the nuclear pore?
A
50kD or 5kD ask someone
13
Q
what are the nuclear import receptors
A
importin part of karyopherin family
14
Q
what is ran GTP
A
small GTP binding protein
15
Q
what is ran GTP
A
smole GTP binding protein
16
Q
what does exportin recognise on the inner membrane?
A
L rich domain
17
Q
what does exportin recognise on the inner membrane?
A
L rich domain
18
Q
types of sorting signal?
A
patch- AAs make patch in 3d form
sequence- AAs at the end of a chain
19
Q
what type of sequence codes for nuclear import?
A
K/R rich
20
Q
what type of sequence codes for mitochondrial import
A
Amphipathic/ alpha helix
21
Q
explain protein import to the mitochondria
A
ATPase Hsp70 in cytosol binds to protein being transported to stop folding proteins signal sequence binds to TOM (Translocon of the Outer Membrane)
protein goes through TOM then TIM (Translocon of the Inner Membrane)
in TIM localisation sequence cleaved by protease, mt Hsp70 binds
Hsp60 also binds helps translocation
22
Q
when is the only time a chemical gradient is needed for protein trafficking
A
across the inner mitochondrial membrane.
23
Q
where can a signalling sequence be recognised
A
membrane bound receptor or soluble receptor
24
Q
where do proteins get synthesised
A
in cytosol ( ribosomes)
25
how do proteins know to go to the nucleus
nuclear localisation signal
26
what makes up the nuclear pore complex
nucleoporin proteins in a basket arrangement
27
what size proteins can fit through the nuclear pore?
50kD or 5kD ask someone
28
what are the nuclear import receptors
importin part of karyopherin family
29
how does the importin work
```
soluble receptor (importin) makes contact with F G (gphenylalanine glycine repeats) importin binds to the protein and takes it through nuclear pore complex
importin and protein dissociat when inside the nucleus
```
30
what is ran GTP
smole GTP binding protein
31
what is the soluble receptor that helps in the export of proteins from the nucleus
EXPORTIN
part of karyopherin family
nuclear export receptor
32
what does exportin recognise on the inner membrane?
L rich domain
33
explain the Ran-GTP cycle
maintans balance between import and export
Ran GDP in cytosol
enters nucleus
interacts with Ran-Guanine nucleotide exchange factor (Ran-GEF) swaps GDP for GTP.
Ran GEF bound to chromatin
Ran-GTP leaves nucleus
hydrolysed by Ran-GAF (ran guanine nucleotide activating factor)
Ran GaP free in cytosol
gradient of Ran GTP to Ran GDP assists import export
34
explain nuclear import
protein with NLF binds to importin
importin contacts FG repeats in nuclear pore complex and takes target protein through the pore
in nucleus Ran GTP binds to importin- displaces the protein being taken to the nucleus
importin moves out of the nucleus
Ran GAP hydrolyses Ran GTP to Ran GDP.
Ran GDP has lower affinity for importin so dissociates.
35
nuclear export
protein with nuclear export signal binds exportin WITH RAN GTP
travels through the membrane binds Ran GAP hydrolyses Ran GTP to Ran GDP which falls off exportin.
exportin goes back through the pore and repeat
36
why and how are proteins unfolded
protein channel much smaller than nuclear pore have to be unfolded to fit
to keep the protein unfolded other proteins bind only folds in mt
37
explain protein import to the mitochondria
proteins signal sequence binds to TOM (Translocon of the Outer Membrane)
protein goes through TOM then TIM (Translocon of the Inner Membrane)
38
when is the only time a chemical gradient is needed for protein trafficking
across the inner mitochondrial membrane.
39
How do proteins get to Outer mt Memebrane
example Porin
binds to TOM kept unfolded in intermembrane space by chaperone
goes through SAM (Sorting and Association Material) (in outer membrane)
SAM helps the protein fold and it diffuses away in the membrane
40
How does an Inner Mt Membrane protein reach the Inner membrane
Protein goes through TOM
goes through TIM
signal sequence cleaved
reveals stop transfer sequence -hydrophobic
stays in the membrane
protein becomes membrane spanning of the inner membrane
41
how does a protein get to the inter membrane space/ inner membrane
attatch to innermembrane with a domain in the inter membrane cells
Goes through TOM
through TIM- signal sequence cleaved uncovers second signal sequence and enters matrix
recognised OXA complex (complex in inner membrane mediates movement of proteins made in mt) and the second signal (hydrophobic) moves laterally in the inner membrane
42
how does a protein get to the inter membrane space
Goes through TOM
through TIM- signal sequence cleaved uncovers second signal sequence and enters matrix
recognised OXA complex (complex in inner membrane mediates movement of proteins made in mt) and the second signal (hydrophobic) moves laterally in the inner membrane
the rest of the protein is cleaved becomes membrane of inter membrane space
43
what is a signal sequence
N terminus
positively charged AA (one or more)
followed by 6-12 hydrophobic AAs
44
what is the SRP
```
Signal recognition particle
in cytosol
has a region that binds to signal sequence and region that binds to ribosome
complex brought to ribosome
complex of 6 proteins and 1 RNA
```
45
what is the SRP R
receptor for SRP recognises SRP+ protein (+ ribosome) on ER membrane- goes through Sec 61- translocon of ER membrane
46
How do proteins get synthesised into ER directly
| cotranslation?
nascent protein plus ribosome binds to SRP brings chain to ribosome which binds SRP R in ER membrane
SRP and SRP R dissociate-
ribosome translates directly into ER
energy comes from hydrolysis of GTP to power the assembly of translocon and chain complex
ribosome translates protein directly into the ER leaving the signal sequence in the membrane which is cleaved
47
post translational movement to the ER
similar to mt
Hsp70 keeps it unfolded
protein directed to Sec62,62,71,72 complex goes through sec 61 channel
Hsp70 or BiP used to pull protein through/stop sliding back
the signal sequence on the protein enters Sec61 and is cleaved by signal peptidases
48
membrane protein of ER
signal into Sec61, cleaved stop sequence remains in membrane difusses laterally
(multiple membrane spanning unit proteins have several stop sequences which remain in the membrane)
49
glycosylation in ER
along with translocation is glycosylation
on asparagine residues
N-X-S
N-X-T
oligosacharyl transferase transfers oligosaccharide to the N residue
utilised to see how far through the translocation process a protein has gone
like a ER tag
50
where do disulphide bridges form
ER
51
explain the rocess of vesicles fusing
1) trans snare complex formed
2) membranes fuse
3) contents released
4) cis snare formed
5) N-ethylmaleimide-sensitive factor (NSF) ( an AAA ATPase)- undoes snare complex dissociates- Alpha snap= accessory to NSF
52
where can a protein go from the ER
endosome, Golgi, lysosome, cell membrane, vesicle
53
function of ER
proteins are glycosylated and folded
54
explain vesicular transport
once the protein has entered the ER it never crosses another membrane
protein coat causes the membrane to bud ( mechanical force)
coat promotes membrane budding
the proteins that go inside the vesicle are specific for the coat
membrane receptors that end up in vesicle act as receptor for target protein.
each coat has a GTP binding domain
snare proteins for assembly/ dissasembly
55
soluble secreted protein
COPII
cis golgi
medial, trans golgi
constutive secretion- regardless of external factors
56
COPI
cis GOLGI to ER
57
Clathrin
trans GOLGI TO ENDOSOME
Plasma membrane to endosome
golgi to lysosme, melanosome or platelet vesicle
58
ER to Cis GOLGI
COPII +
COAT: SEC23/24, SEC13/31, SEC16
GTPase:Sar1
59
cis GOLGI to ER
COPI
Coat:coatomers conatining COP
GTPase:ARF
60
trans GOLGI TO ENDOSOME
either
1) Clathrin + AP1+ ARF
2) Clathrin + GGA+ ARF
61
Plasma membrane to endosome
Clathrin + AP2+ ARF
62
golgi to lysosme, melanosome or platelet vesicle
AP3 + ARF
63
what do GTPases do
control coat recruitment
64
direct fusion
happens between late endosome/lysosme
the 2 compartments fuse to make a hybrid organelle
lysosme specific properties removed in vesicle to switch back
65
Endocytosis
Clathrin coated vesicle at plasma membrane
binds to adapter e.g AP2
clathrin deforms membrane
dynein pinches off vesicle
once vesicle is forme coat dissociates almost immediately
66
what makes sure vesicle binding is specific?
SNAREs
specificity of snares V snares and T snares
need bundle of 4 alpha helices
tetanous toxin cleaves snares
Rab GTP binds to Rab effector on target membrane brings the two together.
leads to the assembly of snares
67
explain the rocess of vesicles fusing
1) trans snare complex formed
2) membranes fuse
3) contents released
4) cis snare formed
68
How do soluble proteins get to the ER
constantly lost and brought back
COPII always takes some soluble ER proteins with it to Cis Golgi
KDEL sequence- ER localisation system
cis GOLGI has recognition for KDEL R
COPI takes KDEL + KDEL R back to ER
ER protein only binds KDEL R in Golgi because it is more acidic there because
69
how do transmembrane proteins get back to ER
Retrieval signal KKXX
CopII takes it to Golgi
CopII brings it back
70
how does a plasma membrane protein reach its target
COPII coated vesicles take what will be a plasma membrane protein to the cis golgi
protein associates with cis golgi membrane
moves to medial then trans golgi
packaged from trans golgi- constitutive secretion
71
soluble secreted protein
COPII
cis golgi
medial, trans golgi
constutive secretion
72
regulated secretion
COPII
golgi
regulated secreted vesicle
need a signal to be released
73
what are the two theories for moving through the golgi
1) vesicular theory- movement of proteins through golgi via vesicles
2)cisternal maturation- cisterna matures and takes on role of neighbouring part . vesicles transfer the characteristic molecules back to new part taking its role
2=favoured
74
getting proteins to the lysosome
lysosome hydralase precursor from ER
phosphate added to manose-> manose-6-phosphate
manose-6-phosphate R in late golgi drawn into clathrin coated vesicle with MP6 receptor in it
vesicle uncoats and taken to late endosome which is kept acidic by ATPase pump causes the dissociation of MP6 and MP6 R
75
O-linked glycosylation
sugar added to -OH group of S T
| catalysed by a series of glycosyl transferase enzymes in golgi
76
without adding mannose 6 P
mucolipidosis type II
| poor growth/skeletal problems
77
endocytosis
LDL through LDLR
| and EGF
