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IMIN 200 > Bacterial Secretion Systems > Flashcards

Bacterial Secretion Systems Flashcards

1
Q

What are the 4 functions of secretion systems?

A

Protection = secrete toxins
Transport of structural proteins
Communication
Adhesion (fimbriae/pili)

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2
Q

What are the two mechanisms of secretion in Gram-negative bacteria?

A

One-step process = across the cell membrane and outer membrane in one step

Two-step process = export into the periplasm (Sec/Tat system) and then export across the outer membrane

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3
Q

What are the secretion systems used in one-step and two-step processes in Gram-negative bacteria?

A

One-step = T3SS, T4SS, T6SS

Two-step = T2SS, T5SS

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4
Q

What is the mechanism of secretion in Gram-positive bacteria?

A

Secreted proteins are commonly translocated across the CM by the Sec pathway or Tat pathway

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5
Q

What does the Sec system do?

A

Translocates unfolded proteins
Recognizes a hydrophobic leader sequence and is present in the cytoplasm of all bacteria

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6
Q

What does the Tat system do?

A

Transport folded proteins
Present in many bacteria and associate with proteins with cofactors

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7
Q

What is the energy source for both the Sec and Tat systems?

A

ATP

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8
Q

What does T1SS do?

A

They are dedicated to transporting one or a few unfolded substrates that range in function
Substrates are generally sec-independent and typically contain a C-terminal signal sequence that is recognized by T1SS and remains uncleaved

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9
Q

What are the 3 major components of the T1SS?

A

ABC transporter
MFP = membrane fusion protein
OMP = outer membrane protein transporter

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10
Q

What does the MFP of T1SS do?

A

Connects and coordinates transport across the CM and the OM

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11
Q

What provides the energy from T1SS?

A

ATP hydrolysis

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12
Q

What do OMFs provide?

A

A trans-periplasmic channel penetrating the outer membrane and connects to the MFP

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13
Q

What connects the OMF and the ABC in the periplasmic space of T1SS?

A

MFP

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14
Q

What does T1SS secrete from UPEC and what does it do?

A

Alpha-hemolysin which allows further invasion of the urinary tract

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15
Q

What is the T1SS toxin, MARTX, secreted from and what does it do?

A

V. cholera
Facilitates colonization of the small intestine by destroying host actin cytoskeleton

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16
Q

What Gram stain is T2SS found in?

A

Gram negative

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17
Q

What is the T2SS also known as and why?

A

The Sec-dependent system
Many proteins that pass through the T2SS must first reach the periplasm via the Sec pathway

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18
Q

Which pathogens require T2SS for virulence?

A

V, cholera, L, pneumonphila, enterotoxigenic E. coli

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19
Q

What are some virulence determinants secreted via the T2SS?

A

The ADP-ribosylating toxins of E. coli
Cholera toxin
Exotoxin A of P. aeruginosa

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20
Q

How does T2SS work?

A

In the CM, there is a platform that anchors T2SS
Unfolded proteins enter the periplasm via Sec and folds in the periplasm
The outer membrane complex is a complex of secretion that transports the folded proteins

21
Q

Which bacteria are type III secretion systems found in?

A

Gram-negative bacteria - both pathogenic and non-pathogenic

22
Q

What is the machinery in type III secretion systems?

A

The injectisome
Delivers effector proteins across bacterial and host membranes into the cytosol of host cells

23
Q

What host cell functions do T3SS secretion systems modulate and how many membranes does it cross?

A

Immune and defense responses
3 membranes, CM + OM + target PM

24
Q

What is the structure of injectisomes?

A

Composed of a series of basal rings that span the bacterial inner and outer membranes and are connected to a hollow needle (in Yersina) or filament (in Salmonella)
Each structure is tipped with a translocation pore that is inserted into the plasma membrane of the target cell

25
Q

What energizes injectisome transport?

A

A conserved ATPase associates with the bacterial base of the injectisome and energizes transport

26
Q

What do the classes of chaperones do to injectisomes?

A

Two classes aid in the assembly of the injectisome
A third class assist in translocation of effector proteins

27
Q

What are many T3SS substrates similar to?

A

Eukaryotic proteins

28
Q

What is the most widespread secretion pathway for the transport of molecules across the outer membrane of Gram-negative bacteria?

A

T5SS

29
Q

What do proteins to be secreted from T5SS contain?

A

Beta barrel structure that insert themselves in the outer membrane

30
Q

How does the protein get through the channel of T5SS?

A

A cleavage separates the channel from the protein to be transported

31
Q

What are some adhesins that are secreted from T5SS?

A

YadA of Yersinia
AIDA-I and Ag43 of E. coli

32
Q

What can be secreted from T5SS?

A

Adhesins, toxins, proteases

33
Q

What is the function of UpaG of UPEC?

A

Adhesin that allows adherence to urinary tract
Promotes bacterial cell aggregation

34
Q

How many membranes does T6SS cross?

A

3 - CM, OM, target membrane

35
Q

What were T6SS and T3SS likely to evolve from?

A

Integrated prophage systems

36
Q

Is there a clear link to virulence in T6SS?

A

No, may be involved in bacterial warfare though

37
Q

What does T6SS constitute?

A

A phage-tail-spike-like injectisome

38
Q

What is used to inject viral DNA into the host by T6SS?

A

A syringe-like process

39
Q

What does T6SS have homology to?

A

Phage neck and tip

40
Q

What is T7SS?

A

A specialized secretion apparatus that is required for the virulence of mycobacteria

41
Q

Where have T7SS gene clusters been found?

A

In the following Gram-positive bacteria
-S. aureus
-L. monocytogenes
-B. subtilis

42
Q

What is the causative agent of tuberculosis?

A

Mycobacterium tuberculosis

43
Q

What does the cell envelope of mycobacteria consist of?

A

A plasma membrane (like an IM)
A periplasmic space that contains peptidoglycan and arabinogalactan
A mycomembrane

44
Q

What are mycomembranes and what do they allow?

A

A thick, complex outer membrane that contains a waxy lipid coat of mycolic acids which allows for immune evasion and resistance to antibiotics

45
Q

How does TB get to its target?

A

It is an airborne pathogen that gets phagocytized by macrophages
The bacteria replicates in the macrophage and dendritic cells then deliver the bacteria to the lymph nodes
Once in the lymph nodes, bacteria can leave cells and enter the blood and leave behind tubercules (scarring) that will restrict respiratory functioning

46
Q

How does TB evade the immune system?

A

During the dormant state, it escapes immune defenses
It inhibits phagosome maturation as well as translocating from the phagolysosomes to the cytosol of the alveolar macrophage
Prevents inflammation

47
Q

What does inhibition of the phagosome

A

Allows replication in endosomes without being trafficked into lysosomes

48
Q

What are 2 substrates of T7SS?

A

ESX-1 = phagosomal escape
ESX-5 = host cell lysis

IMIN 200 (23 decks)

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