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Journey to the Center of the Virus: what SARS-CoV-2 looks like

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Journey to the Center of the Virus: what SARS-CoV-2 looks like

30 Sep, 2020

Coronavirus” is a large family of viruses known to cause illness ranging from the common cold to more serious illness such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).

Coronaviruses were identified in the mid-1960s and are known to infect humans and some animals (including birds and mammals).



Journey_center_virus_SARS-CoV_looks_like_San_Raffaele_University (1)

[The illustration, created by the US Centers for Disease Control and Prevention (CDC), reveals the ultrastructural morphology of SARS-CoV-2. It is possible to notice on the surface the S glycoproteins (in red) that decorate the external surface of the virus, giving it the appearance of a crown (“corona” in Latin, hence the name). Credit: https://phil.cdc.gov/Details.aspx?pid=23312]

 

In December 2019, a new virus belonging to this family, called SARS-CoV-2, was isolated in Wuhan, China. The viral sequence of this new Coronavirus has a homology of approximately 76% compared to the virus that caused the SARS pandemic in 2002/2003, so the two viruses are very similar. How is this virus composed? What structure does it have?

The structure of the "novel Coronavirus"

To analyze its structure we will use the following illustration, which shows a virion (the single viral infectious particle) complete and in section (credit: https://www.scientificanimations.com/wiki-images/).

Journey_center_virus_SARS-CoV_looks_like_San_Raffaele_University (1)

Coronaviruses have a rounded morphology and dimensions of 100-150 nm in diameter (about 600 times smaller than the diameter of a human hair!).

Starting from the outermost layer and progressing gradually towards the inside of the virus, it is possible to notice several components:

  • S (“spike”) Glycoprotein: the virus shows projections on its surface, with a length of about 20 nm. These projections are formed by glycoprotein S (for “spike”). Three S glycoproteins joined together make up a trimer; the trimers of this protein form the structures which, taken together, resemble a corona surrounding the virion. The main differences of this new Coronavirus compared to the SARS virus seem to be located precisely in this spike protein. The glycoprotein S is the one that determines the specificity of the virus for the epithelial cells of the respiratory tract: the 3D model in fact suggests that SARS-CoV-2 is able to bind the ACE2 receptor (angiotensin converting enzyme 2), expressed by the cells of the capillaries of the lungs
  • M-Protein: the membrane protein (M) crosses the envelope interacting within the virion with the RNA-protein complex

Journey_center_virus_SARS-CoV_looks_like_San_Raffaele_University (2)

Scanning microscopy showing SARS-CoV-2 particles emerging from the surface of infected cells. Credit: Rocky Mountain Laboratories (RML), United States National Institute of Allergy and Infectious Diseases (NIAID).
 
  • Hemagglutinin esterase (HE) dimer: this coating protein, smaller than glycoprotein S, plays an important role during the virus release phase inside the host cell
  • E-Protein: the expression of this protein helps glycoprotein S (and therefore the virus) to attach itself to the membrane of the target cell
  • Envelope: it is the envelope of the virus, consisting of a membrane that the virus “inherits” from the host cell after the infection
  • RNA and N-protein: the Coronavirus genome consists of a single strand of RNA with a large positive polarity (from 27 to 32 kb in the different viruses); no larger sized RNA viruses are known. RNA gives rise to 7 viral proteins and is associated with the N protein, which increases its stability

Journey_center_virus_SARS-CoV_looks_like_San_Raffaele_University (3)

Electron microscopy showing SARS-CoV-2 particles emerging from the surface of infected cells. Credit: Rocky Mountain Laboratories (RML), United States National Institute of Allergy and Infectious Diseases (NIAID).
 
 

Want to know how the educational activities of the San Raffaele University will take place according to the anti-Covid legislation? Visit the dedicated section "Info Covid-19" of the Knowledge Base and consult the main questions asked by students

Visit the Info Covid section

Written by

UniSR Communication Team
UniSR Communication Team

Thanks to the contribution of the various team members, the UniSR Marketing and Public Relations Service deals with the multiple communication areas of the University: news scouting, creation of news, audio and video, event organization, website management and institutional social media, drafting and publication of newsletters, support for institutional relations. The Service interacts with all the main stakeholders (students, teachers, technical and administrative staff, research community, territory) in order to support and potential communication (internal and external) of the initiatives related to teaching, research and public engagement.

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