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Bacteriology > Lecture 13 - Bacterial Protein Transport > Flashcards

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
Q

Proteins transported using Usher/Chaperone system

A

Pap pili

Type 1 pili

26
Q 
Usher/Chaperone system
1)
2)
3)
4)
A

1) Peptide translocated using Sec
2) Peptide binds to chaperone
3) Chaperone recognised by usher
4) Usher recognises chaperone, transports peptide

27
Q

Function of chaperone donor strand

A

Inserts into binding groove of transported peptide, prevents it binding to anything

Makes peptide only bind to another subunit of pilus

28
Q

Part of chaperone that prevents premature pilin binding

A

Donor strand

29
Q

Do type I secretion systems use Sec?

A

No

Sec independent

30
Q

What do type I secretion systems normally secrete?

A

Toxins, lipases, proteases

EG: Alpha haemolysin produced by some E coli

31
Q

Type I secretion system signal peptide

A

C-terminal

~60 amino acids in length

32
Q

Parts of type I secretion system
1)
2)
3)

A

1) ATP binding cassette
2) Membrane fusion protein, anchored in cytoplasmic membrane, spans periplasmic space
3) Beta barrel domain

33
Q

Type I secretion system
1)
2)
3)

A

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
Q

Another term for type II secretion system

A

Main terminal branch of general secretory pathway

35
Q

System involved in type 1/Pap pili secretion

A

Chaperone/Usher

36
Q

System involved in type 4 pili secretion

A

Type II secretion system

37
Q

Example of a type 4 pilus

A

Bfp of EPEC

38
Q

Number of proteins involved in a type II secretion system

A

12 - 16 proteins

39
Q

What is the name for the collection of accessory proteins in a type II secretion system?

A

Secreton

40
Q

Outer membrane pore in type II secretion system

A

GspD

41
Q

What is GspD?

A

Outer membrane pore in a type II secretion system

42
Q

Secretin family of proteins
1)
2)
3)

A

1) Form a very stable ring-shaped membrane pores
2) Channel is 5-10nM in diameter
3) EG: GspD

43
Q

Function of GspC

A

Links inner membrane complex to outer membrane pore in a type II secretion system

44
Q

Function of GspS

A

Pilotin
Makes sure that GspD inserts into outer membrane
When absent, GspD inserts into both inner and outer membranes

45
Q

What makes sure that GspD inserts into outer membrane?

A

GspS

46
Q

What links the inner and outer membrane complexes of a type II secretion system?

A

GspC

47
Q

Example of factor secreted by type II secretion system

A

Cholera toxin

48
Q

How is cholera toxin secreted?

A

By a type II secretion system

A and B subunits are secreted through Sec separately, combine in periplasm

49
Q

Type II secretion system signal peptide location

A

N-terminal

Bacteriology (29 decks)

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