Lecture 14: Bacterial and Plant Toxins Flashcards by Tami Ojewole

Toxins are ___

soluble substances that alter the metabolism of host cells with deleterious effects on the host

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Toxins are the ___ factor for pathogenic bacteria

primary virulence factor

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Toxins often require _____ to achieve virulent form

re-arrangement or cleavage

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target of toxins in host cells

cytoplasmic enzymes or structural proteins

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Ricin is from ___

castor bean plant (seed)- plant itself is harmless

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anthrax spores are highly-_____

resistant

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how cholera works generally?

cholera toxin increase cAMP production in intestinal epithelial cells to increase secretion of salts and water, affecting ability to retain water causing diarrhea and dehydration

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toxins serve as tools for cell biologists to reveal ____

new intracellular trafficking pathways

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2 types of toxins

-pore forming toxins
-ab toxins

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pore forming toxins create ____ of host cells

holes in PM

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type of toxin: a-toxin of S.aureus (flesh eating disease)

pore-forming toxin

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a-toxin of S.aureus method

-released by bacterium as 33 kDa protein
-monomers target PM
-forms homo-heptamer form (7 rings)
-inserts in membrane and forms channel
-damge to membrane cause ions to leak out –> swelling + death of cell

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A-chain of ab toxin contains ____

catalytic domain (“toxin” part)

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A-chain of ab toxin modifies ___

cytosolic enzyme

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B-chain of ab toxin is _____

targeting subunit (gets A-chain into cytoplasm)

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B-chain of ab toxin interacts with _____ and guides _____

cell surface receptor (protein, glycolipid or carbohydrate)
A subunit to final destination

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Depending upon toxin, A and B chains are _____

separated by different mechanisms (some no cleavage, some cleavage by bacteria or host cell)

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In all cases, A and B chains of ab toxin require ____ in ____ to separate

-reduction of disulfide bond
cytoplasm of host cell

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Botulinum and tetanus toxins: A chain cleaves____

cleaves specific SNAREs and blocks vesicle targeting and exocytosis

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Botulinum and tetanus toxins: A chain recognize ____

Recognize 9 aa residue motifs unique to SNAREs

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_____recognize different SNAREs and sometimes the same SNAREs at different sites

Different toxins

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Botulinum and tetanus toxins are examples of ___

molecular scalpels

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Cons of Botulinum and tetanus toxins

-block exocytosis
-interrupts neurotransmission (muscle can’t work)

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which type of cells have Botulinum and tetanus toxin receptors?

neuronal (non-neuronal cells don’t have them)

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Pros of Botulinum and tetanus toxins

-inject in or near spastic muscle for relaxation -migraine treatment

“A” subunits of AB Toxins enter cytoplasm via_____

different mechanisms

different ways A subunits enter cytoplasm

-some enter through ER -some enter through endosomes

A-toxin entry in cytoplasm through ER

-endosome->retrograde transport from golgi to ER then enter cytoplasm through Sec61 (retro translocation)

A-toxin entry in cytoplasm through endosomes

-endosome -at low ph (5-6) B chain of toxin becomes hydrophobic and penetrates endosome bilayer -forms channel that translocate unfolded A-chain

AB toxins that entry through endosomes

-cholera, pertussis

AB toxins that entry through ER

-anthrax

____toxins take advantage of retrograde transport pathways in host cells

Shiga and cholera

cons of Shiga and cholera toxins

blocks protein synthesis and kills cells

pros of Shiga and cholera toxins

Identified novel retrograde pathway from endosomes back to ER

Shiga and cholera toxins can be used as markers of ____

retrograde carriers

2 ways to study toxin transport in host cells

1. Genetically modified toxins containing acceptor sites for N-linked glycosylation 2.Fluorescent toxins for live cell imaging

Genetically modifying toxins with acceptor sites for N-linked glycosylation tells us what?

-can deduce where toxin enters cytoplasm -n-glycosylation of toxins doesn't occur in bacterial cells

tagging toxins with fluroresnt atges tells us what?

-Follow movement of fluorescent toxins (or use anti-toxin antibodies) after entering cells -allows us to inhibit specific transport steps

Some toxins gain access to _____ and are transferred to cytoplasm when they reach the ER

secretory pathway by endocytosis

Genetically modifying toxins with acceptor sites for N-linked glycosylation : Shiga toxin

it toxin reaches ER, glycosylation observed (increase in MW)

Glycosylation of toxin can be detected by subjecting cell lysates to _____

SDSPAGE and immunoblotting with antibodies to toxin.

endosome temperature block

19 C

GPP130 is a ____ protein that is important of transport of ___

Golgi-associated shiga toxin

Shiga toxin bypasses _____en route from early endosomes to Golgi?

-late endosomes/lysosomes

GPP130 is a protein that cycles between _____

early endosomes and Golgi

GP73 is a _____ protein that has _____ on toxin transport

Golgi no effect

GPP130 is needed for ____

movement of shiga toxin for endosome to golgi

addition of what salt that induces degradation of GPP130

-Manganese (Mn)

Manganese (Mn) induces ____ in ____

specific degradation of GPP130 in lysosomes

Leupeptin blocks ____

lysosomal degradation of proteins

Manganese (Mn) and shiga toxin trafficking

-rest toxin in endosomes

Manganese (Mn) and cholerat oxin trafficking

-toxin rest in golgi complex

Manganese (Mn) dosing

toxic in high doses, but at lower concentrations, can protectmice from Shiga toxin (prevents kidney damage)

KDEL receptor brings ___

things back to ER

Rab6 brings ___

things back to ER

PM transport temperature block

4 C

STB and Rab6 detected in ___vesicles and tubules

same

STB and KDEL receptor in ___vesicles and tubules

different

Looking transport of STB, KDEL receptor and Rab6 from golgi to ER can __

help us determine how shiga toxin gets from golgi to ER

anti COPI antibodies inhibited movement of _____

KDEL-R containing vesicles

Anti-COPI antibodies had no effect on ___

Rab6-containing vesicles

expression go dominant negative form of protein will __

block function of wildtype protein, prevent function of protein overall

effect of shiga toxin on protein synthesis

Shiga toxin blocks protein synthesis

cells expressing Rab6-DN (dominant negative) have ___

More protein synthesis

delivery of STB to ER from golgi requires ___

Rab6

Toxins enter through ER because ___

>ER contains machinery for unfolding and dislocation of protein (A subunit needs to unfold to thread through Sec 61 in ER)

Toxins aren't degraded by proteasome after retro translocation through Sec61 because _____

degradation by proteasome needed ubiquitination of lysine residues and many toxins don't have lysine residues

Lecture 14: Bacterial and Plant Toxins Flashcards

(67 cards)