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MICR2222 - Medical Virology > L7 - HIV (3) > Flashcards

L7 - HIV (3) Flashcards

1
Q

What are intracellular inhibitors of HIV replication?

A 
TRIM5a
APOBEC3
Tetherin
SAMHD1
SERINC3/5
NONO
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2
Q

What are the 2 alleles/variants of MLV?

A 
N-tropic = N-MLV
B-tropic = B-MLV

infected inbred mice

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3
Q

What was the factor that was tested for in MLV?

A

Fv1 (N or B)

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4
Q

What does Fv1 do?

A

mediated post-entry block to viral replication

blocks from going into the nucleus

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5
Q

What is Fv1?

A

60% homology to MLV capsid protein

single aa change in CA - alters tropism form N to B

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6
Q

What happens when HIV-1 enter a Rhesus monkey cell?

A

blocked BEFORE reverse transcription

cannot be Fv1 as before the reverse transcription

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7
Q

What was the name of the experiment carried to find out why HIV-1 did not replicate in Rhesus monkeys?

A

cell fusion experiment

HIV could NOT replicate in the human/monkey fusions

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8
Q

What was the method for identifying the HIV-1 restriction factor TRIM-5a?

A

cDNA library
transfection
infect with HIV-GFP and select the GFP-neg ones
expand the GFP-neg ones

PCR with specific primers
clone and sequence

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9
Q

What is the HIV-1 restriction factor?

A

TRIM5a

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10
Q

What is TRIM5a?

A
  • RING and B-box = ubiquitination, rapid proteasomal degradation
  • Coiled coils - dimerise
  • SPRY domain - can bind to HIV capsid antigen
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11
Q

What is the structure of the HIV-1 capsid?

A

12 pentamers

215 hexamers

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12
Q

What is the mutation in the Capsid antigen that prevents the TRIM5a block?

A

Mutate Arg110 to Glu

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13
Q

What is the mechanism of TRIM5a restriction?

A

2-stage mechanism

dimerised coiled coil binds to the capsid through SPRY domain - forms net, blocks infection

ubiquitination stops reverse transcription and causes capsid disruption

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14
Q

How does TRIM5a form a net around the capsid?

A

SPRY domains interacts with the capsid

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15
Q

What is the 2-stage mechanism of TRIM5a restriction?

A

infection is blocked due to binding

reverse transcription is blocked due to ubiquitination

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16
Q

How does human TRIM5a NOT block HIV-1?

A

mutation in SPRY domain preventing the interacting with HIV-1 CA

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17
Q

How did HIV-1 cross over from SIVcpz concerning TRIM5a?

A

SIVcpz is NOT blocked by human TRIM5a

18
Q

What is Vif protein?

A

cytoplasmic

192aa

19
Q

What is the function of Vif protein?

A

COUNTERACTS APOBEC3G

affects virus maturation (enhances infectivity)

Binds to virion RNA in cytoplasm - incorporates into virions

20
Q

How was reverse genetics analysis of vif carried out?

A

introduce stop codon

disocvered phenotype of Vif mutant = CELL-TYPE DEPENDENT

NON-INFECTIOUS IN NON-PERMISSIVE CELLS

21
Q

What is the cellular antiviral factor that Vif counteracts?

A

APOBEC3G

22
Q

What is APOBEC3G?

A

ONLY expressed in NON-PERMISSIVE CELLS

cytosine deaminase

deaminates cytosine in uracil

23
Q

What happens to APOBEC3G in the absence of Vif?

A

APOBEC3G incorporated into virus particles

24
Q

What is a non-permissive cell?

A

A cell that does NOT allow the multiplication within it of a virus

25
Q

What does APOBEC3G actually do?

A

deaminates a SINGLE cytosine in APOB mRNA

replaces the NH group with oxygen

convert the CYTOSINE to a URACIL (not normally present in DNA)

HYPERMUTATIONS as you will get base A incorporated into chain instead of G

MISREPLICATION AND DEGRADATION BY ENZYME UNG2 (Ffor when uracil is incorporated into DNA)

26
Q

How does Vif block the action of APOBEC3G?

A

Ubiquitin ligase complex

targets it for proteasomal degradation

27
Q

What is Vpu?

A

81aa

membrane protein

28
Q

What is the function of Vpu?

A

binds to CD4

induces degradation by ubiquitination

Env escapes being trapped in ER

enhances virion release - would get stuck on cell surfaces otherwise

29
Q

Is Vpu present in HIV-1 and HIV-2?

A

NO - only HIV-1

30
Q

How is the phenotype of HIV-1 Vpu mutant cell-type dependent?

A

virus released in permissive cells

virus retained on cell surface in non-permissive cells

31
Q

What is Tetherin?

A

Cell surface protein

blocks enveloped virus release

32
Q

How can tetherin expression be stimulated?

A

IFN treatment

33
Q

How does Vpu interact with tetherin?

A

ubiquitination degradation

34
Q

What does the deletion in the cytoplasmic tail oh human tetherin mean?

A

cannot interact with Nef protein like SIVcpz and SIVgor can

35
Q

Why is M group more successful than HIV-1 O, N & P?

A

HIV-1 M Vpu can interact with tetherin in diff. way as it Nef cannot interact with tetherin and pull it away from membrane

36
Q

What is SAMHD1?

A

^ expressions in myeloid cells

early stage block

only functions in quiescent cells

target for HIV-2 Vpx

37
Q

What autoimmune condition results from mutated SAMHD1?

A

Aicardi-Goutiere Syndrome

dysregulation of IFN system

38
Q

how does SAMHD1 work?

A

dGTP activates

cleaves triphosphate from deoxyribonuceloside triphosphates

removes triphosphate from pool of dNTPs

inhibits REVERSE TRANSCRIPTION

39
Q

What are SERINC 3/5?

A

Serine incorporators

transmembrane

serine into lipids

40
Q

What protein prevents incorporation of SERINC3/5 into virus?

A

Nef

41
Q

What is NONO?

A

Nuclear CAPSID sensor

links to viral DNA sensor - cGAS

WORKS IN THE NUCLEUS

INDUCES INNATE IMMUNE RESPONSE

MICR2222 - Medical Virology (13 decks)

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