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HELENP CBG: Cell Architecture, Communication and Regulation > CBG Lecture 35: Secretory Pathway:Protein Translocation > Flashcards

CBG Lecture 35: Secretory Pathway:Protein Translocation Flashcards

(60 cards)

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1
Q

how does epstein barr virus replicate

A

in an episome

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2
Q

how does EBV survive in a host cell

A

Survives in an infected cell by interfering with the T-cell adhesion response

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3
Q

in what can EBV be reactivated in

A

Can by reactivated in cancers

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4
Q

what do TRIM5 proteins do

A

prevent uncoating of viral capsid proteins

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5
Q

WHAT IS the signal hypothesis

A

signal sequences are typically 15-60aa, oftern @N-terminus, often cleaved by signal peptidases
GUNTER BLOBEL

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6
Q

how long are signals

A

15-60 aa

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7
Q

where does synthesis of all proteins begin

A

in cytoplasm

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8
Q

whatis the signal for ER translocation

A

N-terminal positive…hydrophobic….polar

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9
Q

what is the -3, -1 rule

A

residues @ position -3,-1 relative to cleavage site ,ust be small and neutral (lysine,arg) for cleavage to occur correctly

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10
Q

what is the SRP

A

signal recognition particle

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11
Q

what is Sec

A

a translocon that is an evolnary conserved passive pore

found on ER membrane

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12
Q

name an evolnary conserved passive pore

A

Sec translocon

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13
Q

which Sec in mammals and euks

A

Sec61

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14
Q

which Sec in proks and archaea

A

SecY

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15
Q

discuss structure of Sec translocon

A

heteroetrimeric complex

Sec61alpha, beta, gamma

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16
Q

which monomers of Sec translocon are essential

A

Sec61 alpha and Sec61beta

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17
Q

how is Sec61 a passive pore

A

associating partners provide the driving force
no ATP
depending on partner there are different ways channel could work

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18
Q

what are the Sec modes of action

A

Cotranslational -SecY
Posttranslational eukaryotic - ratcheting
Postranslational bacterial - pushing

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19
Q

what Sec is found exclusively in bacteria

A

SecA

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20
Q

which type of Sec transport requires addditional enerygy

A

brownian ratchet - eukaryotes Sec61

bacterial pushing - SecA

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21
Q

where does energy for cotranslational secretion in Sec come from

A

GTP -> GDP

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22
Q

describe cotranslational Sec61 mode of action

A

protein still being synthesized so pp only has one way to go - energy from GTP hydrolysis

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23
Q

when does postranslational translation happen

A

after protein synthesized - additional energy is necessary - ATP->ADP

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24
Q

discuss cotranslational translocatoin

A

most general mode, most membrane protein translocation

partners include SRP and SRP receptors

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25
what are SRP partners of
cotranslational translocation
26
where does the energy from cotranslational translocation come from
GTP hydrolysis in translation
27
discuss protranslational translation in bacteria
uses SecA the comleted pp chain is fed from the cytosolic side into translocator in the plasma membrane by the Sec A ATPase ATP hydrolysis driven conformational change drives a piston like motion in SecA
28
how are proteins translocated across the ER
by the Sec translocon which is a passive pore
29
what does the mechanism of translocation depend on
interaction partners
30
discuss cotranslational translocation in detail
1. after protein starts to emerge from rib - it may be directed to ER (determined by signal sequence) 2. signal sequence emerges from rib and recognised and bound by an SRP 3. SRP binds rib and signal sequence and stalls translation 4. SRP targets entire complex to RER by binding to an SRP receptor on ER membrane 5. GTP molecules bind to SRP and SRPreceptor - trigers transfer of signal sequence from SRP to Sec61 6. hydrolysis GTP->GDP = dissociation SRP from receptor and the ribosome-mRNA complex 7. transfer of ribosome-mRNA complex to translocon allows the signal sequence to interact with short hydrophobic side chains inside the Sec which oipens the channel by moving the plug away 8. as translocation proceeds - signal is cleaved by signal peptidase, pp freleased into ER lumen
31
how is cotranslational translocation possible
because ribosomes are bound to the ER and not other organelles
32
what is an SRP
Signal Receptor Particle consisting of 6pps and a scmall cytoplasmic RNA
33
what does an SRP do
binds hydrophobic signal on protein
34
discuss post-translational translocation by ratcheting mechanism
ratcheting mechanism -protein first synthesized then transported to ER chaperonin proteins called SecB bind to the pp during synthesis to prevent it from folding prematurely -accessing proteins to fit pp into pore and drive translocation - composed of Sec62,Sec63,Sec71, and Sec72 is attched to the Sec61 and deposits BiP molecules onto the translocating chain as it emerges into the Er lumen ATP driven cycles of BiP binding and release pull the protein into the lumen -unidirectional translocation is driven by cycles of BiP binding and release - Brownian ratchet
35
what is SecB
a chaperonin protein which nbinds to pp in posttranslaitonal translocation to ensrure it doesnt fold up prematuerely
36
what is brownian ratchet
successive binding of BiP-ADO prevents pp backslide back into the cytosol
37
name some cells that use brownian ratchet
yeast and higher eukaryotes
38
how is unidrectional translocation enabled in brownian ratchet
by cycles of BiP binding and release - successive binding of BiP-ADP prevents backslide
39
what is the universal mechanism of initiation of translocation in cotranslational translocation
when signal peptide emerges from ribosome and is recognised by the SRP
40
how does initiation of post translocational translocation happen
after protein synthesis is complete - binding of BiP
41
what is SecY in higher eukaryptes aka
Sec61
42
discuss general architecture of SecY
3 SUs - alpha -helical sand made up of two halves like a clam beta-nonessential as its peripheral gamma transmembrane protein
43
discuss the translocation pore and plug
helical plug of alpha SU blocks the channel in closed state Pore ring lined by hydrophobic residues - gasket like seal crosslinking experiment confirms movement of the plug during translocation
44
why can pp pass laterally through clamp
because it has helical signal sequence enabling ateral passing
45
where is intercalation of signal sequence between
TM2b/TM7
46
discuss the model SecY pore for translocation
confirmed by structures of translocating ribosome - has hourglass shape - helical plug fills middle of channel - pp chain grows from ribosome - signal sequence is alpha helical and intercalates between helices allowing it to displace from membrane so signal peptidase cuts it off
47
how many classes of transmembrane protein are there
4
48
what are the different classes of transpmembrane proteins
1. single pass with cleaved ER signal sequence - N terminus internally 2. single pass INTERNAL SIGNAL SEQUENCE - N-terminus@luminal side 3. INTERNAL SIGNAL SEQUENCE - N terminus @ lumimnal side 4. MULTIPASS TRANSMEMBRANE PROTEINS
49
give some examples of type 1 membrane proteins
``` cleavable signal sequence and downstream sequence glycophorin influenza HA protein insulin receptor growth hormone receptor ```
50
give an example of type 2 membrane protein
transferrin receptor golgi galactosyltransferase influenza HN protein
51
give an example of type 3 receptor
cytochrome P450
52
what type receptor is cytochrome P450
type 3 receptor
53
give an example of a type 4 receptor
GPCR voltage gated Ca2+ Sec61
54
what two types of membrane proteins are basically the same
type 1 and type 3 | type 3 is same as type 1, just with NH3+ on ERgolgi side of membrane
55
what type receptor is a GPCR,VOLTAGE gated Ca2+,Sec61
type 4 transmembrane receptor
56
how is a single pass type 1 TM protein with a cleaved ER signal integrated into the ER membrane
cotranslational translocation and lateral gating | remains as a single alpha helical membrane spanning segment with N terminus on lumenal side and C terminus cytosolic
57
what do topogenic sequences of peptides determine
the orientation in the membrane
58
what part of pp is topogenic sequence
signal anchor sequence
59
how can a topogenic sequence be predicted
by bioinformatics tools
60
what type of TM is a signal-anchor
type 2

HELENP CBG: Cell Architecture, Communication and Regulation (5 decks)

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