Lec 5 - Virus attachment, entry and uncoating

Question 1

What 2 types of interactions are involved in binding of the host receptor?

Answer 1

1. Reversible non-covalent binding
2. Irreversible conformational changes

Question 2

What is affinity?

Answer 2

The strength of binding

Question 3

What is avidity?

Answer 3

The collective strength of all bonds

Question 4

What is used to measure the strength of interaction and what is the typical value?

Answer 4

Dissociation constant K
1x10^-9

Question 5

What type of cell does influenza A virus bind and how?

Answer 5

Epithelial cells of the upper respiratory tract. HA binds sialic acid and NA cleaves this bond for fusion

Question 6

What is the type of sialic acid bound by human vs avian influenza strains?

Answer 6

Human: alpha-2,6-sialic acid
Avian: alpha-2,3-sialic acid

Question 7

How does virus entry by pore formation work?

Answer 7

Virus binds receptors and injects genome through membrane via pore, leaving no spike proteins

Question 8

How does virus entry by fusion work?

Answer 8

Virus binds receptors and fuses with cell membrane by its fusion peptide to release capsid into cell, leaving spike proteins on surface

Question 9

How does clathrin mediated endocytosis work?

Answer 9

Virus enters clathrin coated pit and is endocytosed into vesicle. Acidification by vacuolar ATPase uncoats virus and clathrin is recycled

Question 10

How does caveolae mediated endocytosis work?

Answer 10

Virus enters caveolae coated pit and is endocytosied into vesicle then taken to ER which requires dynamin. ER chaperone proteins uncoat virus

Question 11

What is a 3rd method of endocytosis of viruses?

Answer 11

Phagocytosis by macrophages and neutrophils

Question 12

How do picornaviruses eg poliovirus replicate in harsh environments eg human gut?

Answer 12

Poliovirus has a 4th protein subunit folded beneath the top 3 that’s only revealed after conformational change during binding

Question 13

Where is the viral fusion peptide found?

Answer 13

Viral spike protein after conformational change

Question 14

How does influenza release its genome?

Answer 14

1. Fusion peptide to penetrate membrane
2. Scission to split membrane
3. Apposition to move membrane apart
4. Hemifusion and pore formation

Question 15

How does HIV release its genome?

Answer 15

1. SU/gp120 binds CD4
2. Conformational change so SU/gp120 binds CCR5 or CXCR4
3. TM/gp41’s fusion pepide allows capsid to enter cell

Question 16

List influenza’s main proteins

Answer 16

HA and NA spike proteins
M2 ion channel
RdRp
Nucleoprotein (NP)
Nuclear export protein (NEP)
M1 matrix protein

Question 17

Describe the polarity of microtubules and the proteins used to transport cargo

Answer 17

Positive end at cell periphery and negative end at centrosome/microtubule organising centre (MTOC).
Kineins transport negative to positive
Dyneins transport positive to negative including viral proteins

Question 18

What is the general structure of a nuclear pore complex, and what is required to enter one?

Answer 18

Basket structure on nucleus side, filaments on cytoplasm side.
Need nuclear localisation signal

Question 19

How does adenovirus get its genome the nucleus?

Answer 19

1. Clathrin mediated endocytosis
2. Spike proteins dissociate
3. Protein VI lyses endosome
4. Capsid moves to nucleus by cytoskeleton
5. Conformational changes to capsid and nuclear pore allows entry

Question 20

How does rotavirus evade innate immune receptors inside the cell?

Answer 20

Triple capsid dissociates to double layered particle (DLP) where mRNA is made. NSP1 inhibits NF-kb to inhibit IFN stimulated genes