POLIO

Question 1

What is the structure of polio virus?

Answer 1

-non-enveloped, (+)ssRNA, iscosahedral capsid

Question 2

How does polio get into epithelial cells?

Answer 2

Binds to CD155, which induces endocytosis into cell’s cytoplasm as well as a conformational change in VP1 so it can insert into the lipid bilayer of the host cell
- enters through a pore that is formed

Question 3

How does polio get into the blood stream?

Answer 3

GI track— interstitial tissue— lymphatic system— blood

Question 4

What is the Salk vaccine? What are the advantages and disadvantages of it?

Answer 4

• Inactivated virus
• injected
• advantages: antibody mediated immunity, no potential for reversion, immunosuppressed people can use it
• disadvantages: requires boosters, does not induce antibody mediated immunity in the gut, vaccinated people could still transmit through the gut, expensive,

Question 5

What is the Sabin vaccine?

Answer 5

• attenuated virus (not completely inactivated, but decreased infectivity)
• given orally
• advantages: gut immunity, can immunize an entire household, no booster shot, cheaper
• disadvantages: not good for immunocompromised people, chance of mutation to virulent form, can infect others by shedding a mutated strand through feces

Question 6

What are the four categories of response to a polio infection?

Answer 6

1. Abortive- illness for a few days (95% of cases)
2. Non-paralytic- illness and stiffness in neck for 2-10 days
3. Paralytic- flaccid paralysis following possible illness
4. Post poliomyelitis muscle atrophy- a reappearance of paralysis and muscle wasting decades later

Question 7

Where does paralytic polio attack?

Answer 7

Lower motor neuron

Question 8

How many serotypes are there for polio? What does it bind to?

Answer 8

3; the unique antibody for the serotype

Question 9

What is the epitope that is responsible for neutralizing antibodies?

Answer 9

Sequences on the structural proteins VP1, VP2, VP3

Question 10

What is the arrangement of the virus’ envelope?

Answer 10

60 protomers: each made of three subunits: VP0, VP1, VP3 (180 molecules of protein)

Question 11

What happens when the capsid undergoes a maturation process?

Answer 11

VP0–> VP2 (int) and VP4(ext)

Question 12

What does the genome look like?

Answer 12

• (+)ssRNA, uncapped, VPg is attached to the 5’ end, polyA tail is attached at the 3’ end
• UTR at 5’ end and 3’ (this one is involved in synthesis of (-) strand)

Question 13

What cleaves VPg that was attached to the RNA after entry into the cell?

Answer 13

Cellular enzyme

Question 14

How does polio translate the RNA?

Answer 14

• cells ribosome assembles onto the virus’ RNA using the IRES to initiate translation (instead of the 5’ cap)
• starts 741 nucleotides from the 5’ end
• one ORF is translated to make one large polyprotein
• part of the polyprotein turns into a protease and cleaves it into 20 different proteins
• elF4G cleaves a translation factor needed to make cellular mRNA

Question 15

What are the steps of transcription/replication of RNA?

Answer 15

• VPg and RDRP replicate the genome and synthesize more viral mRNA (replication complex)
• replication complex associates with the membrane structure derived from the ER (replication compartment)
• VPg = primer RDRP for synthesis
• RDRP synthesizes a new (+) strand
• some (+) genomic RNA is used for its proteins, some goes into the virus

Question 16

What are the steps of synthesizing the capsid/genome packaging?

Answer 16

• VP0, VP1, VP3 associate with each other to form the protomer/pentamer
• maturation: VP0 cleaves into VP2 and VP4
• PAC site interacts with the capsid proteins (ensures its the right sense)

Question 17

What are the steps for virus egress?

Answer 17

• genome is inserted into pro-capsid and VP0–> VP2 and VP4 (cleaved by ribozyme)
• one of the encoded proteins is a viroporin that disrupts the plasma membrane by making it more permeable
• cell dies by lysis