Poliovirus Flashcards
Poliovirus
+ssRNA virus from picornavirus family
Baltimore system
virus classification system based on genome structure
Polio route of infection
oral-faecal/respiratory
Difference between virus and virion
Virus is nucleoprotein particle whereas virion is active extracellular vector of virus
Polio virion
30nm diameter
+ssRNA
VPg protein
Covalently attached to 5’UTR of RNA
Act as primer for RNA synthsis or tag
Protein 3B
P1 protein
Capsid structure
Capsid functions
Packaging (RNA protection)
Cell entry (1. receptor binding, entry mechanism
Immune evasion
Capsid proteins
VP0, VP3, VP1
VP0
VP2 + VP4 after cleavage of VP0 for maturation
VP4 myrostylated at N terminus to penetrate cell membrane
Myristylation
14-carbon unsaturated fatty acid, myristic acid, added to the N-terminal glycine of a subset of proteins
Poliovirus pocket factor
lipid base center of capsid proteins - capsid falls apart without it
1 pentamer (polio)
Made up of 5 protomers
1 Capsid (polio)
12 pentamers
Poliovirus receptor and where are they located?
CD155
3 ig-like domains
located on motor neurons, lymph nodes and ileum wall cells
What happens when PV binds to receptor?
Structual change of VP1 induced
Pocket factor released
Destabilisation of capsid
How is PV delivered into the cytoplasm?
VP1 n terminus externalised and forms pore in host cell membrane
RNA delivered through pore by dynamin dependent caveolar endocytosis
Poliovirus A particle
Capsid destabilised and VP4 disassociated from protomers
Internal ribosome entry site structure and function
dsRNA in 5’ UTR of PV genome
6 dsRNA structures with first being cloverleaf involved in translation initiation
binds directly to 40S rsubunit
cap not needed
uses eIF4G fragment
AUG placed in correct position for initiation
eIF4G
part of F cap binding complex
strongly associates with E
cleaved by viral proteases
Why translation of PV ssRNA before replication
To synthesise P2 and P3 proteins needed for replication
PV replication initiation complex (1st)
3CD + polyC binding protein + polyA binding protein
located on 5’ cloverleaf structure
lowers translation efficiency
PolyC binding protein
Required for replication
translational silencing
when 3CDpro binds this increases affinity for PCbp binding
PolyA binding protein
Binds to cloverleaf structure and circularises RNA
CRE (PV) (2nd complex) steps
cis acting replication element
3Dpol + VPg + 3CD
formed on circularised RNA
Replicative form (PV)
positive and negative RNA strands associated together w VPg at 5’ ends
Protein 2C
Helicase of replicative form
Steps in poliovirus replication
7