Lecture 13 - Bacterial Protein Transport Flashcards

1
Q

Transport systems across inner membrane
1)
2)

A

1) Sec translocase

2) Tat

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2
Q

Most complex secretion system

A

G- outer membrane transport

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3
Q

Sec translocase different pathways
1)
2)

A

1) Classical - SecB chaperone

2) Alternative - SRP chaperone

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4
Q
Sec translocase classical pathway
1)
2)
3)
4)
A

1) Peptide translated in ribosome
2) N-terminal signal sequence bound by SecB chaperone
3) SecA recognises chaperone, hydrolyses ATP to pump peptide through SecYEG trimer
4) Signal peptidase removes signal sequence once peptide has been extruded through SecYEG

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5
Q
Sec translocase alternative pathway
1)
2)
3)
4)
A

1) Peptide tarnslated in ribosome
2) Signal sequence recognised by signal recognition particle (SRP)
3) SRP interacts with FTSy.
4) FTSy binds to SecA, secA hydrolyses ATP to pump peptide through SecYEG trimer

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6
Q

Function of YidC

A

YidC is involved in placing membrane-bound proteins in the membrane

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7
Q

Which protein is involved in placement of membrane-bound proteins?

A

YidC

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8
Q

Which proteins make up trimer involved in Sec tranlocation?

A

SecY, SecE, SecG

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9
Q

Sec signal sequence

A

N-terminal signal sequence

~20 amino acids

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10
Q

In what fashion does Sec translocation occur?

A

Stepwise, in groups of 20-30 amino acids at a time

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11
Q
Tat pathway
1)
2)
3)
4)
A

1) Signal sequence binds to TatBC in cell membrane
2) TatBC complexes with TatA
3) TatA is a pore-forming protein, brings a proton into the cell in exchange for extruding bound protein
4) Protein moves through TatABC translocon in a folded state

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12
Q

Pore-forming peptide in Tat pathway

A

TatA

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13
Q

Signal-recognising peptide in Tat pathway

A

TatBC

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14
Q

Difference between Tat and Sec

A

Tat transports natively folded proteins, cofactors can be attached
Sec can only transport unfolded proteins, hence the need for a chaperone molecule

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15
Q

Tat signal sequence

A

N terminal sequence

Twin-arginine motif

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16
Q
Types of outer membrane secretion systems
1)
2)
3)
4)
5)
6)
7)
8)
A

1) Autotransporter (type V)
2) Two partner secretion
3) Chaperone/usher pathway
4) Type I secretion system
5) Type II secretion system
6) Type III secretion system
7) Type IV secretion system
8) Type VI secretion system

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17
Q

Do autotransporters use Sec translocase?

A

Yes

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18
Q

Autotransporter pathway
1)
2)
3)

A

1) Sec translocase brings autotransporter peptide into periplasmic space by recognising signal sequence
2) Beta domain forms beta barrel in outer membrane with assistance of BAM protein
3) Alpha domain is secreted through beta barrel

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19
Q

Domains of a generic autotransporter
1)
2)
3)

A

1) Signal sequence
2) Alpha domain/Passenger domain/Functional domain - Will ultimately act as virulence factor. Can be toxin, protease, adhesin, invasin, etc
3) Beta domain - Forms beta barrel in membrane

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20
Q

On which terminal is a beta domain of an autotransporter?

A

Carboxy-terminal

21
Q

Two partner secretion system

A

Similar concept to autotransporter

Difference is that beta barrel protein is encoded by a different gene

22
Q

Examples of proteins secreted through twin partner secretion system
1)
2)

A

1) Haemolysin from Serratia marcescens

2) Filamentous haemagglutinin in Bordatella pertussis

23
Q

Which system is used to secrete haemolysin and filamentous haemagglutinin?

A

Twin partner secretion system

24
Q

Function of filamentous haemagglutinin

A

Lets B. pertissis bind to beta-1 integrins on lung epithelial cells

Mimics RGD motif on fibronectin

25
Proteins transported using Usher/Chaperone system
Pap pili | Type 1 pili
26
``` Usher/Chaperone system 1) 2) 3) 4) ```
1) Peptide translocated using Sec 2) Peptide binds to chaperone 3) Chaperone recognised by usher 4) Usher recognises chaperone, transports peptide
27
Function of chaperone donor strand
Inserts into binding groove of transported peptide, prevents it binding to anything Makes peptide only bind to another subunit of pilus
28
Part of chaperone that prevents premature pilin binding
Donor strand
29
Do type I secretion systems use Sec?
No | Sec independent
30
What do type I secretion systems normally secrete?
Toxins, lipases, proteases EG: Alpha haemolysin produced by some E coli
31
Type I secretion system signal peptide
C-terminal | ~60 amino acids in length
32
Parts of type I secretion system 1) 2) 3)
1) ATP binding cassette 2) Membrane fusion protein, anchored in cytoplasmic membrane, spans periplasmic space 3) Beta barrel domain
33
Type I secretion system 1) 2) 3)
1) ATP binds to ATP binding cassette 2) Channel of beta barrel opens, membrane fusion protein is pulled down, binds to ATP binding cassette 3) Protein is translocated
34
Another term for type II secretion system
Main terminal branch of general secretory pathway
35
System involved in type 1/Pap pili secretion
Chaperone/Usher
36
System involved in type 4 pili secretion
Type II secretion system
37
Example of a type 4 pilus
Bfp of EPEC
38
Number of proteins involved in a type II secretion system
12 - 16 proteins
39
What is the name for the collection of accessory proteins in a type II secretion system?
Secreton
40
Outer membrane pore in type II secretion system
GspD
41
What is GspD?
Outer membrane pore in a type II secretion system
42
Secretin family of proteins 1) 2) 3)
1) Form a very stable ring-shaped membrane pores 2) Channel is 5-10nM in diameter 3) EG: GspD
43
Function of GspC
Links inner membrane complex to outer membrane pore in a type II secretion system
44
Function of GspS
Pilotin Makes sure that GspD inserts into outer membrane When absent, GspD inserts into both inner and outer membranes
45
What makes sure that GspD inserts into outer membrane?
GspS
46
What links the inner and outer membrane complexes of a type II secretion system?
GspC
47
Example of factor secreted by type II secretion system
Cholera toxin
48
How is cholera toxin secreted?
By a type II secretion system | A and B subunits are secreted through Sec separately, combine in periplasm
49
Type II secretion system signal peptide location
N-terminal