this slides about orthomyxoviruses replication

1. ORTHOMYXOVIRUSES
Edited by
Yousef doozandegan

2. The Influenza Virus
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3. Properties
• Enveloped, helical nucleocapsid
• Contains segmented negative sense RNA
– 8 pieces for types A and B
– 7 pieces for type C
– 6 pieces for thogotovirus , 8 pieces for Isavirus
• Envelope glycoproteins form two types of
spikes
• respiratory transmission
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4. Genome structure of influenza A
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6. Envelope Glycoproteins
• Hemagglutinin ( H antigen)
– Rod-shaped trimers Attack viral protein Required for
viral attachment to sialic acid receptors on
susceptible cells
– Promotes the fusion
– Stimulates formation of protective (neutralizing)
antibody
– Changes due to mutations causing
– Agglutinates erythrocytes in vitro
– Important diagnostic tool
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8. haemagglutinin(HA)
The HA must be enzymatically activated in two subunits: H1 and H2
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10. Envelope Glycoproteins
• Neuraminidase (N antigen)
– tetramer with enzymatic activity
– cleaves sialic acid glycoproteins
– facilitates the release of the virus from infected cells
– target of drugs oseltamivir (Tamiflu)and zanamivir (Relenza)
– mutational changescause variability
– Stimulates production of protective antibodies
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11. • M2 and a Proton Pump
Amantadine specifically
blocks the pump M2 and
is therefore an inhibitor
of influenza virus
replication.
• The histidine 37 and the
tryptophan 41 side
chains form the bottom
of the pore in the closed
state at neutral pH.
M2 protein
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12. The HEF of Influenza C Viruses
• the major glycoprotein of the C viruses has a receptor-
destroying activity.
• In contrast to the HA of influenza A and B viruses.
• About a 12% sequence identity between HAs and HEF.
• In contrast to the neuraminidase activity of the NA proteins of
influenza A and B viruses.
• has esterase activity.
• sequence similarities between the esterases of influenza C
viruses and some coronaviruses.
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14. STAG ES O F VIRAL REPLICATION
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15. Attachment and entry
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16. • Influenza viruses bind to neuraminic acids (sialic acids) on
the surface of cells.
• Human viruses preferentially bind to N-acetylneuraminic
acid attached to the penultimate galactose sugar by an a2,6
linkage (SAa2,6Gal).
• whereas avian viruses mostly bind to sialic acid with an a2,3
linkage.
• Receptor-mediated endocytosis.
• There are four internalization mechanisms:
• (a) via clathrin -coated pits; (b) via caveolae; (c) through
nonclathrin, noncaveolae pathways; and ( d) through
macropinocytosis
• Virus enters cytoplasm in endosome.
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20. Mechanism of clathrin
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21. Mechanism of caveplae
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22. Fusion and uncoating
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23. • Endosome is acidified
• HA conformation change exposes hydrophobic
“fusion peptide”
• Fusion peptide interacts with endosome
membrane and stimulates fusion
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25. • Low pH in endosome activates M2 protein: ion
channel
• M2 allows protons to enter virion
• Acid-induced conformational changes disrupt capsid
• Once membranes have fused, RNA is free to enter
cytoplasm
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28. Nuclear Import of Ribonucleoproteins
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31. Transcription and Replication
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33. THE PB2 PROTEIN
• responsible for binding the cap on host pre mRNA
molecules
• bound to cap analog m7GTP reveals that the cap is
sandwiched between phenylalanine 404 and
histidine 357.
• in influenza B and C virus PB2 proteins, the histidine
is replaced with a more traditional tryptophan.
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34. THE PB1 PROTEIN
• catalyzes the sequential addition of nucleotides
during RNA chain elongation.
• RNA-dependent RNA polymerases(RdRp).
• polymerization activity is an S-D-D motif at positions
444 to 446.
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35. THE PA PROTEIN
• endonuclease activity of the polymerase
• The catalytic site involves residues His 41 ,Glu 80,
Asp 108,Glu 119, and Lys 134 and harbors two
Mn(2+) ions.
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37. transcription
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41. splicing
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43. The Switch from Transcription to
Replication
• the transcription competent polymerase is structurally
different from the replication-competent polymerase.
• The availability of soluble NP (i.e., not associated with RNPs)
controls the switch between mRNA and cRNA synthesis.
• the accumulation of NEP /NS2 is associated with a decrease in
transcription and an increase in replication, suggesting a
regulatory role.(svRNA) 22 to 27 nt
• accumulation of a newly synthesized free polymerase
complex, which enhances cRNA to vRNA synthesis (and vice
versa) over mRNA synthesis.
• The role of host factors.
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44. replication
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48. Nuclear Export of Ribonucleoproteins
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50. Assembly and Release
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51. • RNA segments assemble with replicase and NP in
nucleus
• M2, HA, NA inserted into membrane
• M1 assembles with RNP and directs exit to cytoplasm
• M1 directs assembly with envelope proteins at
membrane
• Budding through membrane
• Hemagglutinin binds sialic acid on surface as virus buds
out
• Neuraminidase cleaves sialic acid to free progeny
virions
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59. H
H1
H2
H3
H4
H5
H6
H7
H8
H9
H10
H11
H12
H13
H14
H15
H16
N
N1
N2
N3
N4
N5
N6
N7
N8
N9
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H N
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