Lecture 4 Flashcards by andrew fleming

What type of membrane do viruses have to overcome to enter animal cells?

How do they achieve this?

Lipidic membrane

Interactions with surface molecules, membrane fusion and transport processes

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What types of virus can attack animal cells?

Both enveloped and non-enveloped

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What type of entry to viruses use to enter animal cells?

What do they deliver into the cell?

Receptor-mediated entry

Delivering nucleic acid and protein shell

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What type membrane do virus have to overcome to enter plant and bacterial cells?

Why is it harder to enter plant cells?

Cell Wall

Plant cell walls have a cellulose cover which is harder to penetrate

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What type of viruses can attack bacteria cells?

Mainly non-enveloped due to the cell wall

But some enveloped phage also exist

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What type of viruses can attack plant cells?

Non-enveloped viruses only

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What type of entry to viruses use to enter bacterial cells?

What do they deliver into the cell?

Receptro mediated entry

Delivery of nucleic acid only by non-enveloped

Enveloped also deliver protein shell

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What type of entry to viruses use to enter plant cells?

Passive entry - Insect injection or mechanical damage

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How do enveloped and non-enveloped viruses rleases their genetic material into the target cell?

Enveloped: Fusion. Membranes fuse and capsid released into cell

Non-enveloped: Form a pore in the cell and inject the nucleic acid (sometimes with a couple of accessory proteins)

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What are the general membrane component targets used by viruses for non-specific binding on animal cells?

Sialic acid and heperan sulfate proteoglycan

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What are the general membrane component targets used by viruses for non-specific binding on bacterial cells?

Lipopolysaccharides on GRAM- and teichoic acids on GRAM+

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What are common families of receptors used by viruses to enter animal cells?

Immunogloblin domains, integrins, GPCRs and c-type lectins

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What are common families of receptors used by viruses to enter bacterial cells?

OmpA, glycolipids and flagella

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How does HIV attach?

Uses heparan sulfate proteoglycan as general target and land attaches to CD4 and a chemokine receptor (co-receptor)

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How does a virus prepare for entry?

Specific conformational and/or strucutral changes

Activated viral intermediate if then formed and is ready for entry.

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Outline how T4 bacteriophage inject their nucleic acid

Firm attachment to LPS achieved

Binding to receptor causes tail sheath contraction and puncture device movement into cytoplasm

Further contraction of tail causes conformational changes to head and removal of plug at base of the head and nucleic acid is released into cytoplasm

How do enveloped phage enter bacterial cells?

Binds to bacterial pilli.

Pilus then retracts pulling the phage to the membrane

The phage undergoes fusion and enzymatically destroys the peptidoglycan layer and pentrates the plasma membrane using the P5 protein which was exposed by loss of its membrane

How do non-enveloped viruses enter animal cells?

Give examples

Cellular factors activate viral particle to create pores

Poliovirus: Binding to receptor causes viral proteins to create pores in cell membrane

Reovirus: Cell cathepsin enzyme alters the capsid and a peptide is released to break the endosomal membrane

Rotavirus: Cell trypsin alters the capsid allowing it to break the endosomal membrane

Adenovirus: Low ph causes viral particle to change capsid structure allowing exit from endosome

How do envelop viruses enter an animal cell?

Envelope viruses often covered in glycoprotein

Binding to receptor causes glycoproteins to insert into membrane of target cell

Glycoproteins will pull membranes together causing fusion

What cell surface components are required for HIV entry?

Which components interact?

Viral glycoproteins (gp120 and gp41), target CD4 and target CCR5/CXCR4

External gp120 trimer binds CD4 and CCR5/CXCR4

Outline the mechanism of HIV membrane fusion

Binding of gp120 to CD4 causes conformational change to allow binding to CCR5/CXCR4. This exposes the fusion peptide on gp41 which can then enter the membrane.

What does influenza bind to on the cell?

Sialic acid

What is required for influenza to fuse membranes?

A low Ph; therefore the influenza virion is taken up by the cell and fuses with endosomal membrane to enter the cytoplasm.

This causes the HA protein to unfold and release the fusion peptide

What other cellular component is important for influenza membrane fusion? Why?

Cellular proteases

Cleavage causes HA1 to extend and cause fusion

Where can membrane fusion of animal viruses happen?

At the cell surface, in endosomes and in the endoplasmic reticulum

Why is the endosomal entry of HIV contraversial?

What internalisation pathway do adenovirus and influenza use?

Clathirin-mediated

What internalisation pathway does SV40 use? Why?

Caveosome - a pH neutral vesicle. The caveosome will bring it close to the microtubules which it can use to reach the ER and finally the nucleus

How do viruses use the cytoskeleton to move?

The virus/the endosome carrying the virus will bind to dynein and be transported down microtubules towards the nucleus

Why do viruses not use phagocytosis?

The virus is too small to be phagocysed

How does ebola enter the cell?

Usually macropinocytosis but can also use clathrin-mediated endocytosis

What about ebolas glycoprotein makes it difficult to treat?

The glycoprotein can bind to a large range of different targets

How is ebola entry into the cell similar to influenza entry? What additional factor is required?

Requires low pH and proteases; cleaving gp1 and freeing the fusiogenic tail Endosomal membrane protein NCP1; a 14 tansmembrane domain protein, that has yet to be found. Which is important for gp1 removal.

When is the capsid removed from adenovirus?

At the nuclear pore

How does HIV use the host for its integration?

If the reversed transcribed DNA was just released in cytoplasm it would be degraded, so HIV uses cellular components to help transport the DNA to the nucleus to be integrated

What is the main way the body stop viruses getitng into the tissue?

Mucosa

What cells does HIV target?

The immune cells surveying the mucosa; T cells, macrophages and monocytes

Which cells take up HIV but are not infected? Why is this still dangerous?

Dendritic cells will take up HIV via lectin but do not get infected Instead they carru the HIV and present it to the actual target cells

Which inhibitors exist for HIV?

CCR5 inhibitor; only targets CCR5 HIV, cannot target CXCR4 becuase it is crucial for many important processes T-20 fusion inhibitor; mimics gp41 to intefere with HIV. Mainly for drug-resistant strains.