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MICR2121 Molecular Virology > Virus Assembly & Release 2 > Flashcards

Virus Assembly & Release 2 Flashcards

1
Q

What type of virus is HIV?

A

Retrovirus

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2
Q

How big is the RNA genome of HIV?

A

9.5 +ve RNA genome

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3
Q

Where does HIV assembly take place?

A

plasma membrane

intracellular vesicles

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4
Q

How are HIV virions released?

A

budding

non-cytopathic

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5
Q

What are components of the HIV virion?

A

Gag Pol Env

  • gp41, gp120
  • 2 x ssRNA(+)
  • p24, p7, p17, p6
  • accessory proteins
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6
Q

How do retroviruses (HIV) express their structural proteins?

A

Gag Pol Env

  • 5’ LTR drives transcription
  • ribosome falls off at end of pol
  • Splice donor/acceptor
  • GagPol is removed leaving shortened RNA encoding only Env
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7
Q

How does frameshift occur to make Gag-Pol?

A
  • change frame at end of Gag
  • change frame into ORF which codes for Pol protein
  • bypass stop codon to produce fusion protein
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8
Q

Why do you only want a small amount (5%) of Gag-Pol fusion protein

A
  • pol makes enzymes, do not need much

- gag is a structural protein

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9
Q

What are the 4 proteins made by Gag

A

MA matrix antigen
CA capsid antigen
NC nucelocapsid
p6

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10
Q

What are the 3 proteins made by Gag-pol?

A

Protease
Reverse transcriptase
Integrase

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11
Q

How is Gag targeted to membranes?

A

myristate does NOT interact with aa sequences
myristate inserts into bilayer
stabilised by electrostatic interaction

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12
Q

How is Env expressed?

A
  • Env protein to membrane
  • ribosome binds to SRP
  • signal peptide cleaved off by signal peptidase
  • cleavage of gp160 to gp41 and gp120 by furin
  • disulfide bond & trimerise
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13
Q

How is genomic RNA incorporated into the HIV virion?

A
  • packaging signal after LTR
  • 4 stem loops
  • bound by NC (p7) of p55Gag
  • motif Cys-Cys-His-Cys (similar to zinc-finger)
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14
Q

How do immature HIV capsids assemble?

A
  • 1500 p55 molecules assemble at membrane
  • can occur in cell-free system
  • form in insect & human cells but NOT yeast or murine (cellular factors important)
  • ATP
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15
Q

How does cellular trafficking occur via multi-vesicular bodies?

A
  • clathrin coated pit
  • early endosome
  • MVB
  • exosomes - contain viral mRNA and glycoproteins on surfaces
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16
Q

How does the glycoprotein move to outside surface in the MVB?

A
  • trimer interacts with clathrin due to targeting sequence in gp41
  • when buds through, becomes on outside when membrane is pushed through to make the vesicles
17
Q

What is the ESCRT?

A
  • 30-40 cellular proteins
  • get material into MVBs
  • HIV can interact with components
18
Q

How does HIV Gag recruit the ESCRT complex?

A
  • p6 - PTAP late domain
  • interacts with ESCRT complex
  • Gag accumulates with ESCRT complex on cytoplasmic face of MVB
  • Gag buds into MVB
19
Q

How does HIV release occur via MVBs?

A
  • MVB fuse with membrane
  • non cytopathic
  • normal cellular mechanism
20
Q

What other way apart from MVBS can HIV be released?

A
  • budding from plasma membrane
    Gag recruits ESCRT to plasma membrane
  • may involve lipid rafts
21
Q

How does cellular trafficking occur via multi-vesicular bodies?

A
  • clathrin coated pit
  • early endosome
  • MVB
  • exosomes - contain viral mRNA and glycoproteins on surfaces
22
Q

How does the glycoprotein move to outside surface in the MVB?

A
  • trimer interacts with clathrin due to targeting sequence in gp41
  • when buds through, becomes on outside when membrane is pushed through to make the vesicles
23
Q

What is the ESCRT?

A
  • 30-40 cellular proteins
  • get material into MVBs
  • HIV can interact with components
24
Q

How does HIV Gag recruit the ESCRT complex?

A
  • p6 - PTAP late domain
  • interacts with ESCRT complex
  • Gag accumulates with ESCRT complex on cytoplasmic face of MVB
  • Gag buds into MVB
25
Q

How does HIV release occur via MVBs?

A
  • MVB fuse with membrane
  • non cytopathic
  • normal cellular mechanism
26
Q

What other way apart from MVBS can HIV be released?

A
  • budding from plasma membrane
27
Q

What are the accessory proteins incorporated into HIV-1 virions?

A
  • Vpr - interacts with p6 (infectivity)
  • Vif - binds RNA (infectivity)
  • Nef - myristolated (infectivity)
28
Q

What cellular proteins are incorporated into HIV particles?

A
  • CyPA - peptidyl-prolyl isomerase
  • target for immunosuppressive drug cyclosporin A
  • incorporates MHC Class I
29
Q

What are the similarities of HIV and poliovirus assembly?

A
  • myristolation of structural proteins (VP4 vs p17MA)
  • proteolytic cleavage of polyprotein
  • membrane structures for assembly

MICR2121 Molecular Virology (15 decks)

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