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MICR 221 > Lecture 14 > Flashcards

Lecture 14 Flashcards

1
Q

Define “Exotoxins” (general):

A

Exotoxins: proteins deliberately secreted by pathogens
- they disrupt the host cell

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2
Q

Name a mechanism by which bacterial infections spread?

A

Exotoxins

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3
Q

What were the 3 groups of exotoxins listed in class - Name

A
  • AB toxins
  • Pore-forming toxins
  • Superantigens
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4
Q

Describe the mechanism/ components of AB toxins

A
  • AB toxins interfere with processes inside the host cell
  • It is a complex composed of 2 components:
    A : active component
    B: binding component
  • B: binds to a receptor on the host cell, triggering endocytosis which helps the A component enter
  • A: is an enzyme which is the cause of the toxic effect
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5
Q

“Diphtheria Toxin” was an example of?

A

Diphtheria Toxin = AB toxin

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6
Q

Describe the mechanism of Diphtheria Toxin infection.
What does this toxin damage?

A
  • Note this is an AB toxin
    1) The B chain attaches to a receptor on the host cell membrane
    2) The B component activates Endocytosis
    3) The A component is released from the vacuole into the cell
    4) The A factor:
  • modified elongation factor
  • blocks translation
    note: 1 toxin can modify all EF-2 in cell

This toxin damages:
- cardiac and nerve tissue

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7
Q

Describe the mechanism and target of “Shiga Toxin”

A
  • Shiga Toxin is an AB toxin
  • Enters host cells using B component
  • The A component targets the ribosome
  • A component removes a nucleobase from rRNA, disabling the ribosome
  • Causes damage to vascular endothelium, leads to inflammation and GI bleeding
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8
Q

Describe the mechanism of pore forming toxins

A

Pore forming toxins are a type of AB toxins
- they insert into the host cell membrane, forming channels
- this disrupts the ion gradient and cytoplasmic contents leak out
- water enters the cells and it swells
- the cell is lysed
- lysis of the host cell releases nutrients and helps bacteria escape from phagosomes

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9
Q

What bacterium was used as an example of lysis

A

Hemolysins: toxins that lyse RBCs
- bacteria then scavenge the released heme/iron

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10
Q

Listeria Monocytogenes - Describe

A

Listeria Monocytogenes
- pore-forming toxin section
- are intracellular pathogens
- After they escape (via lysis) they replication in immune cells
- they spread through blood causing bacterial meningitis

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11
Q

True or False:
Superantigens only bind cells together if an antigen is present

A

False - Superantigens bind the cells together even if no antigen is present

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12
Q

Describe the process/mechanism of ‘Superantigens’

A
  • Phagocytes, like macrophages engulf bacterium and present the antigen on its surface
  • DC’s present antigens to T cells
  • Superantigens bind these cells together, even when no antigen is present
  • this triggers over production of proinflammatory cytokines
  • (over reaction of the immune system)
  • Leads to fever, low bp, organ failure
  • ex. TSS
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13
Q

What fraction of bacterial proteins leave the cytoplasm?

A

1 in 3

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14
Q

Define: Translocation

A

Translocation: transport across membrane
- also: insertion into membrane

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15
Q

Define: Secretion

A

Secretion: release into external environment
- requires translocation through 1 or 2 membranes

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16
Q

What is a ‘signal peptide’ and when is it important/used?

A
  • Translocated/secreted proteins often have signal peptides
  • These are specific amino acid sequences at the N-terminus
  • they are recognized by transport systems
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17
Q

Proteins are translocated to the periplasm by: Name the 3 mechanisms

A
  • Sec system
  • Tat system
  • ABC exporters
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18
Q

What/where does the sec system transport?

A

The sec system transports unfolded proteins into the periplasm

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19
Q

What proteins binds the signal peptide?

A

SecA binds the signal peptide

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20
Q

Describe - Sec System: Post-Translational Translocation

A
  • The Sec system translocates unfolded proteins into the periplasm
  • chaperones stabilize the proteins before translation
  • SecA binds to signal peptide, escorts proteins to SecYEG
  • SecA drives translocation of protein through SecYEG (uses ATP)
  • Post-translational translocation occurs after translation is complete
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21
Q

Describe what happens in the Sec System once the protein is in the periplasm?

A
  • Signal peptidase recognizes, and cuts signal peptide during translocation
  • The translocated protein folds in the periplasm with the help of periplasmic chaperones
    -Disulfide bonds are formed bc the periplasm is an oxidizing environment
22
Q

Fill in the blank: The cytoplasm is a _______ environment and the periplasm is a _______ environment

A

The cytoplasm is a reducing environment and the periplasm is a oxidizing environment

23
Q

Where are Tat system proteins folded?

A

The tat system translocates folded proteins from the cytoplasm to the periplasm

24
Q

What 3 things may be required for the tat system?

A
  • Co-factor insertion
  • Cytoplasmic chaperons
  • Assembly into complexes
25
Q

Describe the mechanism of the tat system

A
  • the protein is folded in the cytoplasm
  • folded protein is targeted to TatABC by signal peptide
  • TatABC translocates the protein into the periplasm using the proton motor force for energy
  • the signal protein is cleaved off
26
Q

What are ABC transporters used for?

A

ABC
- primary active transport = use ATP
- specific

ABC importers
- substances in like nutrients

ABC exporters
- waste, antibiotics
- proteins (recognize signal peptide, cleave SP during export)

27
Q

proteins in the membrane are usually ______

A

proteins in the membrane are usually hydrophobic

28
Q

All transporters are inserted into the membrane using the ____ system

A

All transporters are inserted into the membrane using the sec system

29
Q

How do Sec Systems insert proteins into the membrane?

A
  • The signal peptidase is translated first, this is very hydrophobic for a membrane protein
  • The signal peptide is recognized by signal recognition particle
  • This halts translation
  • The signal recognition particle delivers the ribosome to SecYEG
  • Translation continues, inserting the protein into the membrane
    -= Co-translational translocation
30
Q

Describe the process of the Gram-Negative BAM complex

A
  • B-barrel proteins are targeted to the outer membrane
  • The unfolded protein is translocated by the Sec system
  • It is stabilized by periplasmic chaperones (SurA, Skp)
  • Delivered to B-barrel assembly machinery (BAM) complex
  • inserts into membrane
31
Q

Gram-Negative Secretion System - Proteins can be:

A

Gram-Negative Secretion System - Proteins can be:
- bound to cell surface
- released into the external environment
- injected into other cells

32
Q

Describe Type V Secretion System

A
  • Tat or Sec system translocates the protein into the periplasm
  • The protein is translocated through B-barrel in the outer membrane
  • The B-barrel can be: a separate protein or a part of the protein being translated
33
Q

What are the 3 components and their functions in a T1SS

A

ABC transporter:
- powers transport
- determines specificity
B-barrel protein:
- forms a channel thru the outer membrane
Membrane Fusion Protein (MFP):
- connects ABC transporter to B-barrel

34
Q

What is the purpose of T3SS

A

To inject proteins into eukaryotic cells

35
Q

Which secretion system has effector proteins and what do they do?

A

T3SS have effector proteins
- Effectors manipulate host cell structure and function, facilitating colonization

36
Q

How are T3SS’s assembled?

A
  • they consist of a basal body and a needle/filament tip
  • during assembly, subunits (needle, tip) travel through the hollow central channel
  • After assembly is complete, a plug blocks the channel
37
Q

Describe how an effector uses a T3SS to get into the target protein

A
  • Once the T3SS binds the target, the channel opens
  • Chaperones deliver unfolded effectors to T3SS
  • The Effector travels through T3SS, and folds in the target
  • The transport is powered by ATP and the PMF
  • Note: a single T3SS secretes different effectors, they are recognized by N-terminal secretion signal
38
Q

T3SS Effector Proteins
Target:
Function:

A

T3SS Effector Proteins
Target: effectors target host cytoskeleton, signal transduction

Function: they rearrange the cytoskeleton of epithelia cells, forming surface ‘ruffles’ which allows bacteria to enter cells that are normally non-phagocytic

39
Q

What is the purpose of efflux pumps?

A

To transport molecules to the periplasm or outside the cell

40
Q

Name 2 classes of efflux pumps

A
  • ABC transporters
  • RND tripartite system
41
Q

Name a major contributor to multidrug resistance?

A

Efflux pumps

42
Q

Define: Extracellular Vesicles

A

Extracellular Vesicles: spherical buds released from cell surface used by bacteria to export substances

43
Q

“Outer membrane vesicles” are the term used to describe extracellular vesicles released by ____ ___

A

“Outer membrane vesicles” are the term used to describe extracellular vesicles released by gram negative bacteria

44
Q

Name 3 things extracellular vesicles contribute to:

A
  • HGT
  • Virulence
  • Antibiotic resistance
45
Q

What example was given for Ev’s and Antibiotic Resistance

A
  • Gram-Negative EV’s containing B-lactamases
  • B-lactam enters EV through porins
  • B-lactamases in EV degrade B-lactam
  • Keeps B-lactams away from PBPs
46
Q

What makes gram-positive protein secretion easier

A
  • no outer membrane
  • does not need elaborate secretion system
47
Q

Which secretion systems are used by gram-positive bacteria

A

Tat and Sec systems

48
Q

What does Sortase do?

A

Sortase - attaches proteins that have cell wall sorting signals to the cell’s surface

49
Q

Name 4 functions of Gram-positive surface proteins

A
  1. often contribute to virulence
  2. used to attach to host cells extracellular matrix
  3. Nutrient acquisition in host
  4. Immune evasion
50
Q
A

MICR 221 (12 decks)

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