CBG Lecture 35: Secretory Pathway:Protein Translocation Flashcards Preview

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Flashcards in CBG Lecture 35: Secretory Pathway:Protein Translocation Deck (60)
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1

how does epstein barr virus replicate

in an episome

2

how does EBV survive in a host cell

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

3

in what can EBV be reactivated in

Can by reactivated in cancers

4

what do TRIM5 proteins do

prevent uncoating of viral capsid proteins

5

WHAT IS the signal hypothesis

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

6

how long are signals

15-60 aa

7

where does synthesis of all proteins begin

in cytoplasm

8

whatis the signal for ER translocation

N-terminal positive...hydrophobic....polar

9

what is the -3, -1 rule

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

10

what is the SRP

signal recognition particle

11

what is Sec

a translocon that is an evolnary conserved passive pore
found on ER membrane

12

name an evolnary conserved passive pore

Sec translocon

13

which Sec in mammals and euks

Sec61

14

which Sec in proks and archaea

SecY

15

discuss structure of Sec translocon

heteroetrimeric complex
Sec61alpha, beta, gamma

16

which monomers of Sec translocon are essential

Sec61 alpha and Sec61beta

17

how is Sec61 a passive pore

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

18

what are the Sec modes of action

Cotranslational -SecY
Posttranslational eukaryotic - ratcheting
Postranslational bacterial - pushing

19

what Sec is found exclusively in bacteria

SecA

20

which type of Sec transport requires addditional enerygy

brownian ratchet - eukaryotes Sec61
bacterial pushing - SecA

21

where does energy for cotranslational secretion in Sec come from

GTP -> GDP

22

describe cotranslational Sec61 mode of action

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

23

when does postranslational translation happen

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

24

discuss cotranslational translocatoin

most general mode, most membrane protein translocation
partners include SRP and SRP receptors

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