Magor- Lecture 3: Virus entry into cells

Question 1

TRUE or FALSE
Viral entry is passive

Answer 1

FALSE.
Viral entry is not passive.

Question 2

The entry process of virus can facilitate ________

Answer 2

uncoating.
The genetic material outside of capsid is part of the process

Question 3

Viruses _________(can/cannot) pass freely through membrane (in either direction.

Answer 3

cannot

The plasma membrane is impermeable

Question 4

Glycoproteins

Answer 4

proteins on the outside of a cell

Many virus receptors are proteins (often glycoproteins) on the host cell

Question 5

Phagocytosis
define and steps

Answer 5

• Macrophages use phagocytosis to take up bacteria and viruses.

1. Large particles are engulfed by a phagocytic cell, such as a macrophage.
2. Extensions fuse around the particle
3. Phagosome fuse with lysosomes and the particles are destroyed.

Question 6

Viruses use a specific type of endocytosis called

Answer 6

receptor-mediated endocytosis

Question 7

Steps of Receptor mediated endocytosis (in this case for a virus)

Answer 7

1. Virus binds to a cell surface receptor. This diffuses into an invagination coated with clathrin.
2. The clathrin pit pinches off forming a ‘coated vesicle’.
3. The clathrin uncoats the vesicle.
4. The vesicle fuses with the early endosome. The early endosome is acidic.
5. The acidification releases the virus from the receptor, and receptor is returned to the cell surface.

Question 8

Viruses use proteins on the host cell as __________

Answer 8

receptors

Question 9

Rhinovirus (common cold) and poliovirus are related _____________

Answer 9

picornaviruses

Question 10

Pvr

Answer 10

• poliovirus receptor
• involved in DC-NK (dendritic cell-natural killer) interactions
• also present on erythrocytes

Question 11

Icam-1

Answer 11

• Intracellular adhesion molecule-1
• Rhinovirus receptor
• involved in macrophage T-cell interactions

Question 12

Rhinovirus

Answer 12

• cause the common cold
• more than 90 related serotypes -types not recognized by some antibodies.

Question 13

Presence of ___________ determines specificity of virus host range (tropism)

Answer 13

receptor

Ex: mice do not have Pvr and are not infected with poliovirus. Human and mouse ICAM-1 are different enough that rhinoviruses cannot infect mice. They had to put human receptor in mice for experiments

Question 14

entry of non-enveloped virus:
Human rhinovirus entry and uncoating

Answer 14

1. The virus attached to ICam-1 and enters by endocytosis.
2. The acidic environment of the endosome causes the uncoating of the particle (rhinovirus is sensitive to acid in endosome)
3. The RNA is released into the cytoplasm
4. Icam-1 deep in canyon facilitates destabilization of capsid

Question 15

Difference of rhinovirus and poliovirus (in terms of resistance)

Answer 15

Rhinovirus is not resistant to acid, unlike poliovirus

Question 16

Icam-1 binds deep within the __________ of rhinovirus

Answer 16

‘canyon’

Question 17

Why is it significant that the receptor binding site is recessed?

Answer 17

It is inaccessible to antibodies, it’s blocked

Question 18

What happens after neutralizing antibodies?

Answer 18

Neutralizing antibody blocks binding of the receptor to the canyon.

Question 19

Where on ICAM-1 does rhinovirus bind?

Answer 19

D1

Question 20

In ICAM-1, the binding sites for _________ and _________ overlap

Answer 20

LFA-1 and human rhinovirus (HRV)

Question 21

Poliovirus can be transmitted through:

Answer 21

fecal/oral

Question 22

Is Poliovirus acid-resistant?

Answer 22

yes

Question 23

Pvr interaction causes major ______________

Answer 23

structural changes

Question 24

Formation of a pore in the membrane by poliovirus

Answer 24

1. Interaction with Pvr causes a major structural change.
2. the N termini of the VP1 protein extends into the membrane.
3. This may form a pore in which the RNA can enter.

Question 25

__________________ internalization of poliovirus (say by a macrophage) doe snot allow uncoating

Answer 25

Fc-receptor mediated

Question 26

Membrane fusion is a highly regulated process involving proteins for __________ and ____________.

Answer 26

targeting and docking

Question 27

Fusogens

Answer 27

• enveloped viruses encode their own fusogens
• protein involved in joining 2 membranes together
• also called fusogenic peptide
  -hydrophobic

Question 28

___________ is the cellular receptor for influenza virus attachment

Answer 28

Sialic acid

Question 29

________________ are the receptors for influenza binding

Answer 29

Integral membrane glycoproteins

Question 30

Entry of an enveloped virus: Influenza

Answer 30

1. Influenza virus hemagglutinin (HA) binds to terminal sialic acid.
2. Human influenza HA prefers to bind to an α (2,6) linked sialic acid.
3. Fusogenic peptide is exposed by an acid catalyzed structural change
4. Virus RNA is inside two membranes. To get out, it uses its fusogen.
5. Acidic environment of the endosome causes conformational change in HA
6. Conformational changes in HA2 expose fusogenic peptide

Question 31

HA

Answer 31

• globular domain that binds to the sialic acid

Question 32

Hemagglutinin (HA) is activated wen cleaved into _____ and ______.

Answer 32

HA1 and HA2

Question 33

Acid catalyzation happens in ______

Answer 33

HA2

Question 34

After acid catalyzation, influenza hemagglutinin conformational change expose the _____________

Answer 34

fusogenic peptide

Question 35

Further structural changes in HA induce ____________

Answer 35

membrane fusion

Question 36

ACE2 receptor

Answer 36

• SARS-CoV2 uses ACE2 receptor for entry
• Angiotensin converting enzyme 2
• functional receptor that acts as an entry point into human lung cells for coronaviruses such as SARS and novel coronavirus SARS-CoV2

Question 37

polybasic cleavage site -site cleaved by furin is unique in this virus

Answer 37

SARS-CoV2