Flu life cycle Flashcards
Dominant H1N5 strain in N. America
B3.13
Concern of spread of dominant strain of H15N
Cattle human interaction
What do influenza virus A infect
Humans, pigs, birds, horses, aquatic mammals
Which type of infleunza virus causes global pandemics
Type A
Influenza B infects what host
Humans
Influenza virus C infects what host
Human and pig
Infleunza virus D infects what host
Humans and pigs
Describe morphology of influenza virus
Pleomorphic virus particles
Occasional rod-shaped elongated particles
Three membrane proteins, Na, H2 and M2
M1 lies where in the virion
Inside
M2 lies where on the virion
Membrane channel
M2 is ___amer
Tetramer
NA is a ___mer
Tetramer
HA is a ___mer
Trimer
Is influenza negative or positive sense
Negative
Are the 8 segments linear or circular
Linear
What complexes are the segments assembled into
RNA-protein complexes called RNPs
What do the strands of influenza look like in the virus particle
Hairpins
What are the flu RNA strands held together by what two interactions
- Canonical Watson-Crick interactions forming between 5’ and 3’ nt, these are complementary.
- 5’ and3’ ends interact with a complex of three proteins called RdRp.
What viral proteins covers the RNA forming a chain and involved in forming RNPs
Nucleoprotein NP
Chain formation of NP requires on two properties
- NP-NP interaction via the tail loop (tail loop of NP interacts with an adjacent NP)
- RNA binding within a groove on the NP surface which is lined with +ve charged a.a such as lys and arg. Electrostatic interaction to the backbone.
Influenza virus RNPs are further folded into what configuration, what holds these strands
Double RNA helices, they are antiparallel held together by NP-NP interactions
What makes up the RdRp of infleunza
PB1, PB2 and PA
What two genes are spliced
M into M2 and NS into NS2/NEP
NS1 function
Non-structural protein 1: IFN antagonist, RNP export
Ns2/NEP function
Non structural protein 2: RNA export (spliced)
M1 function
Matrix protein
M2 function
Ion channel
Are some additional protein products made during infection, what abundance
Yes, low abundance
Describe the 8 steps of the influenza life cycle
- Virus binds SA receptor via HA, interanlisation
- Low pH induced membrane fusion via Ha
- Segments released into cytoplasm
- Segments imported into nucleus
- RNA synthesis
- RNA/RNP export
- Virus assembly at plasma membrane
- Release
Virus attatchment is mediated by what protein
HA
Sialic acid is present on what cells
Epithelial cells, especially ciliated epithelial cells, mainly found in LTR also URT
Sialic acid is linked to galactose in what two ways
alpha2-3 or alpha2-6 linkages
The infectivity of cells is dependent on what linkage
Sialic acid
Human infleunza viruses mainly infect cells which what type of SA linkage
Alpha 2-6
Avian influenza viruses mainly infect cells with what SA linkage
Alpha2-3
Describe structure and formation of HA
Initially synthesised as HA0
Assembled into trimer
HA0 cleaved –> HA1, HA2
Ha1 forms globular head, receptor binding
HA2 forms long stalk via 6 helix bunle
Cleavage of HA0 is mediated by what
Cellular proteases
After binding SA is internalised into what structure
Endosome
What does fusion allow for
RNP segments to be released
HA contains what peptide
Fusion peptide
Inside the endosome due to low pH what conformational change is triggered
two helices in HA2 become aligned this flips the fusion peptide upwards and so the fusion peptide inserts itself into the endosome membrane. Further pH-induced changes brings the 2 membranes together.
HA two functions in life cycle
Virus attatchment
Virus entry
RNP release is mediated by what protein, how
M2, influx of H+/K+ ions so matrix later breaks down
Where does RNA synthesis occurs
Nucleus
RNPs are too big to diffuse into the nucleus, how are they imported
there is an active transport process for RNP import. Individual NP monomers have 2 import signals, only NLS1 is exposed on formed RNPs. NLS1 recruits importin-alpha, which recruits importin-beta. RNP/importin complex binds pore and enters nucleus.
What two processes is RNA synthesis split into
Transcription and replication
Describe infleunza virus polymerase interactions with host factors
PB2 interacts with ANP32 to form an asymmetric dimer, the interaction is necessary for polymerase activity.
Describe 4 stages of transcription
- RdRp PB2 binds a cellular mRNA in the nucleus and PA steals its 5’ cap
- RdRp and capped oligonucleotide bind to negative stranded RNA genome
- RdRp PB1 uses the capped RNA to begin transcription, gets incorporated
- RdRp moves along template, PB1 generates a RNA transcript with a 5’ cap and a 3’ poly (A) tail – mRNA is not encapsidated
Does transcription or replication occur first
Transcription
Describe process of replication, 4 steps
1.RdRp binds 3’ end of the RNA segment, no primer needed
2. RdRp travels along the segment 3’ to 5’ generating a complimentary copy
3. NP wraps the RNA as it is made – so replication products are RNPs
4. Cycles of replication allow amplification of genomes
Why does transcription occur first
NP is needed for replication
RNA export involves the binding of _____ and _____
Involves binding of M1 and NS2/NEP
In RNA export what do RNPs associate with
Multiple copies of M1
Do all RNP associated proteins have import signals
Yes
NS2 binds M forming _______, and why
Outer layer on RNP; has an export singal which dominates all other signals
What is RNP export mediated by C_____
This is mediated via a protein called CRM1 which binds Ran-GTP and exist NPC.
All 8RNPs much reach the a_____ surface membrane, alongisde the 4 strucutral proteins
Apical
In the cytoplasm are the mRNAs translated and they move down what pathway
The mRNAs are translated in the ER then the proteins are trafficked via secretory pathway.
The location of the 8 segments of RNPs follows what arragement X+Y
7+1
Virion formation involves the plasma membrane doing what;
Virion formation involved curving the PM around the 8 RNP segments.
Curvature of the plasma membrane is due to…
Curvature is caused by combination event of HA, NA, M1
Pinching off involves depolorisation of the membrane, what protein directs this
M2
Does influenza use ESCRT
NO
Function of NA
Cleaves sialic acid on previously infected cell, allowing further infection
