FN - Antiphage Mechanisms

Question 1

What are the 4 main virus resistance mechanisms?

Answer 1

1. Preventing virus adsorption
2. Preventing virus DNA entry
3. Cutting virus nucleic acids
4. Abortive infection

Question 2

What 3 mechanisms are involved in preventing virus adsorption?

Answer 2

• Blocking virus receptors
• Production of extracellular matrix
• Host mutating virus receptors

Question 3

What is an example of preventing virus adsorption?

Answer 3

Tail protein J → LamB (maltose uptake)

Tail protein J (1 mut) → LamB*

• 8 days of co-culturing in a strain with low lamB expression

Tail protein J (4 mut) → LamB and OmpF

Question 4

What does blcking virus receptors encompass? (3)

Answer 4

1. Host mutates receptor
2. Virus recognises mutated receptor
3. Host masks receptor

Question 5

How does the production of extracellular matrix prevent virus adsorption?

Answer 5

Host produces EPS (extracellular polysaccharides)

→ Virus produces EPS degrading enzymes (polysaccharide lyase/hydrolase)

Question 6

What does the superinfection exclusion state?

Answer 6

Viruses prevent that the same cell is infected by the same or different virus (lysogens)

Question 7

What does preventing virus DNA entry involve? (2)

Answer 7

1. T4 lysozyme degrades Peptidoglycan
2. phage proteins Imm and Sp block entry

Question 8

What does Imm and Sp cause?

Answer 8

Imm - redirects DNA

Sp - blocks T4 lysozyme

Question 9

What is the principle behind cutting virus nucleic acids?

Answer 9

Host DNA is modified and protected from cleavage, virus DNA is not

Question 10

What are the 3 adaptations related to the restriction / modification systems (R/M systems)?

Answer 10

→ Virus adaptation – modify nucleotides

→ Host adaptation – modify nuclease (R)

→ Virus adaptation – anti-restriction proteins

Question 11

What are the 2 main abortive infections?

Answer 11

1. Membrane puncturing
2. Self toxification

Question 12

Describe the mechanism of membrane puncturing? (3)

Answer 12

1) phage DNA replication / recombination detected by RexA

2) RexA activated

3) RexB allows escape of + ions

• Membrane potential lost
• ATP synthesis blocked

Question 13

What causes self-toxification?

Answer 13

Upon phage infection, toxin inhibits essential host protein for example: DNA gyrase

Virus infection alters AntiToxin-Toxin balance
(by shutting down host transcription)

→ more toxin than antitoxin
→ self toxification