Lecture 15- Influenza Flashcards

1
Q

The Influenza Virion

A

M1- the matrix protein:
Tightly bound to each protein segment, on the inside of the envelope. Structural role and also binds to segments to shut off replication in the late infection phase
NEP: Present in the virion, not associated with RNA segments; nuclear export protein
M2: ion channel. Embedded in lipid bilayer; has a pore to let ions flow in and out of virion.
RNA pol: associated with each of the 8 segments.
NA: cleaves sialic acid off of proteins
HA: virion attachment protein. Receptor is the carbohydrate sialic acid.

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2
Q

PB2

A

transcription, cap snatching

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3
Q

PB1

A

Rna polymerase

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4
Q

PA

A

accessory protein, endonuclease

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5
Q

HA

A

virion attachment protein

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6
Q

NA

A

cleaves sialic acid off glycoproteins

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7
Q

M1

A

matrix protein, from genome segment/mRNA 7

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8
Q

M2

A

ion channel

made from spliced 7 mRNA

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9
Q

NEP

A

(NS2) nuclear export protein

made from spliced 8 mRNA

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10
Q

Influenza RNP

A

Ribonucleoprotein (RNP)

consists of genome segment associated with NP, PB1, PA, and PB2

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11
Q

Adsorption and Entry

A

HA attaches to sialic acid on glycoproteins (sialic acid containing receptors)
enters by receptor mediated endocytosis
results in endosomal vesicle
low pH of endosome activates M2 ion channel resulting in flow of protons into the interior of virion. The resulting low pH of the virion core alters M1 and causes M1 to dissociate from RNP particles. so acidification of endosome occurs as well as membrane fusion and youre left with just segments attached to rna pol.
NP has nuclear targeting signal, which results in it getting brought to the nucleus.

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12
Q

Hemagglutinin and receptor-mediated endocytosis

A

Synthesis and processing of HA:
HA0 is cleaved in the middle by golgi process. This creates HA1 and HA2, which are connected by a disulfide bond.
HA1 has a sialic acid binding pocket
HA2 has a fusion peptide on the N terminus (close to C term of HA1) which fuses envelope with endosomal membrane. Also has TM region on C terminus- trimerizes in the membrane of the golgi.
Conformational change of HA induced by low pH:
Neutral pH form of (HA)3
Sialic acid binding pocket up at the top, binds to sialic acid in the plasma membrane. Fusion peptide is tucked away, unneeded near viral envelope.
Upon acidification of endosome ( low pH form of (HA)3))
Sialic acid binding pockets tucked away, fusion peptide brought out to top. Fusion peptide protrudes: promotes fusion event to release nucleocapsids.

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13
Q

Transcription vs Replication

A

Transcription requires PB1, PA, PB2
(PB1 = polymerase)
Have a segment with a UC at 3’ end and a 5’ end, NPs coating the - strand RNA.
Add PB1/PB2, PA complex
Add Cellular mRNA including 5’ cap
PB complex binds to 3’ end
PB2 recruits cellular mRNA that has 5’ cap (in nucleus)
PB2 captures end of the mRNA. PA has endonuclease activity: cleaves 10-13 nt from 5’ end by PA. generally after an A residue
PB2 continues to hold onto cap (PA just chills from now on)
A pairs with U at the very 3’ end of - RNA
PB1 uses this snatched cap to start synthesis!
addition of NTPs results in + viral mRNA (no NP)
Transcription stops about 15-22 nucleotides from 5’ end of template: sequence of seven U’s
Stutters to make poly A tail
wind up with + viral mRNA (no NP)
NP protein does not block access to template- actually helps!

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14
Q

Replication: (requires PB1, PA, and NP)

A
  • strand genome RNA coated with NP
    add on PB1/PB2/PA complex
    PA in the presence of NP protein, promotes initiation
    PA promotes initiation at 3’ end of template without the need for a primer
    requires NP to coat nascent chain. otherwise replication would abort and wait until there was enough NP
    wind up with + nascent antigenome coated with NP
    At the end: full length + antigenome coated with NP; no poly A
    distinguishing between this and transcription is NP protein, and PA (endonuclease vs promoting initiation)
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15
Q

Assembly and release

A

M1 protein binds to RNPs and blocks both transcription and replication
NEP bound to segments as well, plus RNA pol
NEP protein binds to RNPs after M1.
leaves nucleus, M1 on inside of plasma membrane and HA and NA embedded in lipid bilayer
get budding.
NA removes sialic acid from NA, HA and plasma membrane proteins. Removes sialic acid from surrounding viruses too! This prevents clumping

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16
Q

Mechanism of packaging for influenza

A

Principles of assembly for influenza:

1) Each virion contains one of each of the 8 different segments
2) 5’ and 3’ sequences in RNA segments required for proper packaging
3) viral proteins may interact with RNA ends to sequentially build the cylindrical bundle containing 8 segments.