Influenza Part1 Wk4

Question 1

Family = orthomyxoviridae (7 genera)
Baltimore class V
=ssRNA of negative (-) sense

Answer 1

Segmented genomes
- 7 influenza C & D strains
- 8 influenza A & B strains

Question 2

Humans infected by members of … genus

Answer 2

Alphainfluenzavirus influenza A viruses

Betainfluenzavirus influenza B viruses

Gammainfluenzavirus influenza C virus

Question 3

Structure

Question 4

Haemagglutinin protein = complex structure

Answer 4

^ is translated in infected cells as single polyprotein = HAo
Cleaved in the ER of infected cell during replication cycle
Cleavage occurs at surface loop structure
= 2 proteins
HA1 = surface attachment protein
HA2 = transmembrane fusion protein

Question 5

Following cleavage, 2 proteins linked by a disulphide bridge
Associate as a trimetric structure within membranes
HA1

Answer 5

(surface attachment protein) is glycosylated in Golgi
Major target of host immune responses - vaccine component

Question 6

HA2 transmembrane fusion protein

Answer 6

Anchors proteins in cell membrane & virus envelope

Contains membrane fusion peptide, hidden & inactive at neutral pH

Short cytoplasmic tail binds with M1 matrix protein

Question 7

Host cell proteases are target for therapeutic drugs
decanoyl-RVKR -chloromethylketone
hexa-D-arginine amide
Naphthofluorescein
SSM 3 trifluoroacetate

Answer 7

Peptide mimetic block furin protease - inhibit influenza and SARS
Therapeutic potential for range of other virus infectious diseases, cancers + inflammatory or autoimmune disorders

Question 8

Influenza A subtypes defined by HA and NA proteins
Antigenic type or genus A,B,C + subtype is reflected in nomenclature

Answer 8

Influenza A / chicken / Hong Kong / 220 / 97 (H5N1)
Genus / species / location of isolate / isolate number / year of isolation haemagglutinin (H) & neuraminidase (N) subtypes (influenza A viruses)
ONLY FOR INFLUENZA A H&N antigen forms part of descriptor

Question 9

Segmented genomes - A&B viruses have 8 segments
3 largest segments a code enzymes of the RNA polymerase enzyme (transcriptase)

Answer 9

PB2 = cap binding peptide
PB1 = RNA polymerase
PA = ribonuclease

Question 10

4 segments encoded structual proteins of vision

Answer 10

HA = haemagglutinin
NP = nucleoprotein
NA= neuraminidase
M= Matrix1 & Matrix2

Question 11

Smallest segment encodes

Answer 11

Non-structual protein 1
= RNA transport, translation, splicing
Non-structual protein 2
= nuclear export protein (NEP)

Question 12

Segmented genomes - C & D have 7 segments

Answer 12

Most encode same major proteins, only have 1 envelope glycoprotein
= Haemagglutinin Esterase Fusion

Question 13

Each genomic segment binds a copy of RNA polymerase

Answer 13

Complementary sequences in 3’-UTR and 5’UTR anneal to form a dsRNA terminal region
dsRNA region binds to RNA polymerase enzyme
Remainder of ssRNA binds with NP nucleoprotein, forming a helical structure, ribonucleoprotein (RNP) core
Nucleocapsid - 8 inside matrix layer of a virion
(No true capsid)

Question 14

Influenza A virus replication cycle - attachment

Answer 14

Terminal galactose-neuraminic (Sialic) acid disaccharides form attachment site

Question 15

HA1 proteins in A & B viruses attach to N-linked galactose-sialic acid on cell surface proteins
HEF proteins on C virus attached to O-linked Galactose-sialic acid

Answer 15

O-linked glycans- first monosaccharide links to oxygen atom of Serine of Threonine residues
N-linked glycans = first monosaccharide in side chain links to the amide atom (N) of Asparagine in motifs
Ask-X-Ser or Asn-X-Thr

Question 16

Human A virus HA1 proteins attach to alpha 2-6 linked galactose-sialic acid
-dominant on epithelial cell surface proteins in human upper respiratory tract

Answer 16

Avian influenza A virus HA1 proteins attach to alpha 2-3 linked galactose-sialic acid
-dominant on epithelial cell surface proteins in the avian gut (& respiratory) tracts AND the human lower respiratory tract

Question 17

Human receptor

Question 18

Avian receptor

Question 19

A replication cycle - penetration & uncoating

Answer 19

HA1 binding to cell ‘receptor’ = endocytosis

Question 20

Acidification of endoscope triggers membrane fusion

Answer 20

Neural pH
HA1 protein masks HA2 protein
NA2 fusion domains are hidden in trimmer core
HA2 anchored in virus envelop

Acidic pH (~pH5-6)
HA1 head rotates aside
NA2 fusion domains emerge from core
Interact with endosome membrane

Question 21

Low pH causes conformational changes in the HA2 peptide (exposed from protein core)
HA2 proteins resold into a hairpin structure
Pulls virus envelope and the endosome membrane together

Answer 21

Outer phospholipid layers of 2 membranes rearrange, starting fusion process.
Region of phospholipid rearrangement extends, outer phospholipid layer also rearranges

Question 22

Acidification of endosome triggers genome release (uncoating)
Rearrangement of phospholipid layers = merging of endosome and virus membranes = pore

Answer 22

Virus M2 proteins = ion (proton) channel = import H+ ions from endosome lumen into virus core.
Low pH weakens interactions between M1 matrix protein and NP protein of vRNPs = release (uncoating) of vRNPs from virus core
Virus genome segments (as vRNPs) exit the endosome, enter cytoplasm & traffic to the cell nucleus

Question 23

HA2 and M2 proteins are targets for antiviral drugs
HA2 fusion peptide inhibitors
Block virus penetration

Answer 23

M2 ion channel inhibitors
Block uncoating step

Question 24

Influenza A virus replication cycle - RNA transcription & replication

Answer 24

Transcription = positive sense mRNAs for protein translation
^= positive sense RNA = template for RNA transcription to produce negative sense RNA genomes