Lecture 14 Flashcards by Julia Huomo

Define “Exotoxins” (general):

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

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Name a mechanism by which bacterial infections spread?

Exotoxins

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

AB toxins
Pore-forming toxins
Superantigens

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Describe the mechanism/ components of AB toxins

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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“Diphtheria Toxin” was an example of?

Diphtheria Toxin = AB toxin

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

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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Describe the mechanism and target of “Shiga Toxin”

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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Describe the mechanism of pore forming toxins

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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What bacterium was used as an example of lysis

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

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Listeria Monocytogenes - Describe

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

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

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Describe the process/mechanism of ‘Superantigens’

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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What fraction of bacterial proteins leave the cytoplasm?

1 in 3

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Define: Translocation

Translocation: transport across membrane
- also: insertion into membrane

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Define: Secretion

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

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

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

Sec system
Tat system
ABC exporters

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What/where does the sec system transport?

The sec system transports unfolded proteins into the periplasm

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What proteins binds the signal peptide?

SecA binds the signal peptide

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Describe - Sec System: Post-Translational Translocation

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

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

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

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

Where are Tat system proteins folded?

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

What 3 things may be required for the tat system?

Co-factor insertion
Cytoplasmic chaperons
Assembly into complexes

Describe the mechanism of the tat system

- 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

What are ABC transporters used for?

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)

proteins in the membrane are usually ______

proteins in the membrane are usually hydrophobic

All transporters are inserted into the membrane using the ____ system

All transporters are inserted into the membrane using the sec system

How do Sec Systems insert proteins into the membrane?

- 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

Describe the process of the Gram-Negative BAM complex

- 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

Gram-Negative Secretion System - Proteins can be:

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

Describe Type V Secretion System

- 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

What are the 3 components and their functions in a T1SS

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

What is the purpose of T3SS

To inject proteins into eukaryotic cells

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

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

How are T3SS's assembled?

- 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

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

- 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

T3SS Effector Proteins Target: Function:

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

What is the purpose of efflux pumps?

To transport molecules to the periplasm or outside the cell

Name 2 classes of efflux pumps

- ABC transporters - RND tripartite system

Name a major contributor to multidrug resistance?

Efflux pumps

Define: Extracellular Vesicles

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

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

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

Name 3 things extracellular vesicles contribute to:

- HGT - Virulence - Antibiotic resistance

What example was given for Ev's and Antibiotic Resistance

- 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

What makes gram-positive protein secretion easier

- no outer membrane - does not need elaborate secretion system

Which secretion systems are used by gram-positive bacteria

Tat and Sec systems

What does Sortase do?

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

Name 4 functions of Gram-positive surface proteins

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