# Picornaviridae (Bengihan Gündoğan)

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**Bengihan Gündoğan - 1605A055**
***Picornaviridae***
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# Picornaviridae

#### Picornavirus is a nonenveloped, positive strand RNA virus. Pico means in latin language *"small"*. It describes small RNA viruses.

<img src="https://i.imgur.com/kgUwUUK.png" width="600" height="150" />

#### Table 1. Some distinctive features of Picornavirus.

* **Classification of Picornavirus**
1. Aphthovirus (Causes: *Foot-and-mouth disease*)
2. Cardiovirus (Causes: *Encephalomyocarditis*)
3. Enterovirus (Causes: *Poliomyelitis*)
4. Hepatovirus (Causes: *Hepatitis A*)
5. Senecavirus

**Enterovirus has subspecies such as Poliovirus, Coxsackievirus, Rhinovirus and causes different diseases according to the tissue it attaches to.**

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## Virion Shape as follows:


#### Figure 1. An icosahedral schematic diagram of the capsid structure of the polio virus is shown. Viral RNA is packaged in the capsid at the 5' ends of the VPg-bound genome. VP1, VP2 and VP3 creates the assembly subunit. VP4 does not contribute to capsid symmetry.

* **Poliovirus has positive polarity and 7.5 kb single-stranded RNA.**

* **Virion RNA (vRNA) itself is known "Infectious" because when transfected into cells it can lead to progeny virus production. "Infectivity" of viral genomic RNA is a feature of positive-stranded RNA viruses.**

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## RNA genome structure of poliovirus

<img src="https://i.imgur.com/fT9lmwU.png" width="700" height="350" />

#### Figure 2. The 3' end of the RNA genome has a poly(A) tail. The 5' NCR contains two cis-acting elements such as the cloverleaf structure and IRES.

<img src="https://i.imgur.com/STX4WWN.png" width="650" height="175" />

#### Table 2. Poliovirus proteins and their functions.

* **The vRNA (viral genomic RNA) itself acts as mRNA, a feature that is characteristic of positive sense RNA viruses. vRNA encodes a large protein called a polyprotein. It is then cleaved into functional proteins together with the viral protease. to proteins such as P1, P2, and P3.**

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## Life cyle of Poliovirus


#### Figure 3. Life cycle of Poliovirus.

* **The poliovirus capsid enters the cell via receptor-mediated endocytosis. The important point to be noted for the polio virus is the life cycle of the virus limited to the cytoplasm.**

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## Entry of Poliovirus

<img src="https://i.imgur.com/sp1RwBX.png" width="500" height="500" />

#### Figure 4. Shows how Poliovirus enter the cell. Poliovirus uses the CD155 receptor (Pvr).


#### Table 3. Different kinds of Virus and used receptors. [Vincent Racaniello](https://www.youtube.com/watch?v=k3p_H_-G6Nc)

* **Interesting point is here, different kinds of viruses as PRV (Pseudorabiesvirus) and BHV (Bovine Herpesvirus) uses the same receptor with Picornavirus.**

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## Cleavage of VPg-RNA linkage


#### Figure 5. Cleavage by VPg

* **After entry, VPg bound to the 5' terminus of polioviral RNA cleavage occurs, catalyzed by cellular TDP2. The phosphodiester bond between the tyrosine (Y) residue of VPg and the first U residue of viral RNA, is divided.**

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## Translation


#### Figure 6. Translation Mechanism of Poliovirus

* **In eukaryotic cells, translation proceeds in a cap-dependent manner. However, RNA The 5' end of the picornavirus genome lacks a cap structure. Therefore, the presence of the ribosome's IRES element becomes important. It enters RNA internally on viral RNA and as opposed to its 5' end for translation. This is the translation start mode It is called “title-free translation”. As the polyprotein is translated, it is processed by the viral 2APRO. It yields the P1 and P2 polypeptides and then obtains multiple individual proteins with 3CPRO.**

[Source: NCBI](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3535308/)

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## Proteolytic processing of Poliovirus polyprotein


#### Figure 7. Shows proteolytic process of polyprotein into other proteins.

* **Question mark denotes it is not known which protease cleave the VP0 into VP4 and VP2.**

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## Genome Replication


#### Figure 8. Genome Replication Mechanism of Poliovirus

* **RNA genome replication of poliovirus follows the strategy of positive-stranded RNA viruses. Negative strand RNA is synthesized using vRNA as template and then the newly formed negative-stranded RNA serves as a template for positive-stranded RNA synthesis. Genomic RNA is a template for RNA genome replication as well as translation. The mechanism that apparently streamlines them competitive processes are defined.**

[Source: Viralzone](https://viralzone.expasy.org/1116)

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## Circularization of the RNA genome


#### Figure 9. Shows how circle could occur.

* **3CDPRO binds not only to 3' NCR but also 5' NCR (Non-coding Region). Second, PCBP [poly (rC) binding protein], which binds to the clover-leaf structure at 50 NCR, interacts with PABP [poly (rA) binding protein] at 3' NCR. The circularization of RNA genome was also reported in other positive-strand RNA viruses such as flaviviruses (eg, Dengue virus, Hepatitis C virus, and Japanese encephalitis virus).**

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## Negative-Strand RNA Synthesis


#### Figure 10. Comparing Poliovirus and Hepatitis B virus and Adenovirus

* **A salient feature of picornavirus RNA genome replication is that RNA synthesis begins with protein preparation. In other words, a protein (VPg) rather than nucleotide acts as a primer for RNA synthesis by 3DPOL. Specifically, the hydroxyl group of a tyrosine residue of the VPg peptide is first nucleotide UTP, a process called VPg uridylylation. As a result, the VPg-bound oligonucleotide (VPgpUpUOH) synthesized. Following the cleavage of the 3AB precursor to VPg by 3CPRO, RNA synthesis continues. to obtain a full-length negative-stranded RNA. It is noteworthy that protein preparation occurs in relation to the vesicular. Dice with 3AB precursor attached. Membrane-associated RNA genome replication is almost all positive-stranded RNA viruses.**

[Source: Researchgate](https://www.researchgate.net/publication/12280575_Identification_of_an_RNA_Hairpin_in_Poliovirus_RNA_That_Serves_as_the_Primary_Template_in_the_In_Vitro_Uridylylation_of_VPg)

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## Protein Priming by Poliovirus 3DPOL


#### Figure 11. Initiation of RNA synthesis by 3DPOL is initiated by an associated 3AB precursor. With vesicular membrane (eg, endoplasmic reticulum). Nucleophilic attack by a hydroxyl group of a tyrosine residue, the 3AB precursor of the first U residue. VPg-linked RNA is released from the membrane following cleavage by 3CPRO.

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## Positive-Strand RNA Synthesis


#### Figure 12. Synthesis of Positive strand RNA

* **Surprisingly, CRE (cis-acting replication element) is required for positive-stranded RNA synthesis; Note, however, that this item is not required for the following. Negative strand RNA synthesis. Similar to negative strand RNA synthesis, VPg-linked oligonucleotide (VPg-pUpUOH) is first synthesized via protein preparation. Unlike negative strand RNA synthesis, synthesis of the VPg-UU primer is templated by a CRE element located in the middle of the RNA genome. Next, a VPg-UU primer it displaces the 3' end of the negative-stranded RNA and then resumes RNA synthesis.**

[Source: Plos Pathogens](https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1000936)

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## The RNA genome replication of the poliovirus


#### Figure 13. Initiation of RNA synthesis is templated by the 3' poly(A) tail, while initiation of RNA synthesis is templated by the CRE element. The translocation of the VPg-UU primer from the CRE to the 3' end of the RNA is indicated by dashed lines. The CRE element holding the hairpin structure encodes the "AA" residues in the loop region of the hairpin. Newly formed RNA is colored the newly formed RNA is colored in red and the newly formed RNA in blue.

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## Assembly and Release


#### Figure 14. Assembly and Release Mechanism of Poliovirus

* **The capsid assembly is formed when the building blocks for the capsid assembly accumulate. proteolytic Cleavage of the P1 precursor leads to the formation of a 5S structural subunit called the protomer of VP01VP31VP1. Next, the 14S pentamers are assembled by arranging five 5S units. recognition Adaptation of genomic RNA by 14S pentamers drives not only RNA packaging but also 150S provirion assembly. Provirion is not contagious even though it contains the RNA genome. Conjoined poliovirus particles (provirion) released through cell lysis. Finally, proteolytic cleavage of VP0 to VP41VP2 occurs after viral release.The process is called "maturation," which gives the virion "infectivity."**

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## Life Cycle of Picornavirus in Brief
* **In Carl Gunther's video briefly mentioned of life cycle of Picornavirus.**

{%youtube _uDKQSELyno%}

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## Vaccines to Poliovirus


#### Table 4. Comparement of Polio Vaccines (OPV and IPV)

* **Sabine vaccine is a live but attenuated vaccine. And weakened simply means reduced effectiveness. So the vaccine itself is actually effective. With three doses of vaccine 95% effectiveness. The Salk vaccine is the killed version of the virus. So it can't even reproduce. And this is a very effective vaccine. So it's about 90% effective with just one dose, and is 99% effective after three doses. And the other key difference between the two is that the Sabin vaccine is a liquid medicine, meaning it comes in a bottle of liquid and you can drink it. When injecting Salk vaccine, it is considered intramuscular. It is injected intramuscularly through a needle, through a syringe. There is a lot of difference between these two. The benefit of the Sabin vaccine is that it induces both. humoral and cell-mediated immunity. Whereas the Salk vaccine really only induces humoral immunity. In other words, there is no cell-mediated immunity with the Salk vaccine.**

[Source: Researchgate](https://www.researchgate.net/publication/26837546_Time_for_a_Worldwide_Shift_from_Oral_Polio_Vaccine_to_Inactivated_Polio_Vaccine)

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## Dr. Jonas Salk


#### Figure 15. Jonas Salk the Inventor of Polio Vaccine

* **One question often asked is why did he, as an inventor of the vaccine, not patent his invention? In a famous 1955 interview of Jonas Salk, Edward Murrow asked him who owned the patent. Jonas Salk’s reply:**

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**“Well, the people, I would say. There is no patent. Could you patent the sun?**
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[Source: ipeg.com](https://www.ipeg.com/jonas-salk-inventor-of-the-polio-vaccine-could-you-patent-the-sun/)

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## Interesting study with Poliovirus

### Treatment of Glioblastoma with Poliovirus


#### Figure 16. An engineered type 1 IRES with the conserved, cryptic AUG initiating a foreign ORF mimicking the predicted overall structure of the HRV IRES SLD VI.

* **The treatment is a form of the poliovirus vaccine, genetically engineered to preferentially hunt down tumor cells. It is delivered straight into the brain tumor via a surgically implanted catheter. It works by killing cancer cells and simultaneously triggering an immune response against the tumor. PVSRIPO is the commercial name of drug.**

[Source: New England Journal of Magazine](https://www.nejm.org/doi/full/10.1056/NEJMoa1716435)
[Source: Nature](https://www.nature.com/articles/s41467-019-13939-z)

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