Researchers of Semmelweis University were able to study the structure of the active and infectious coronavirus in collaboration with the researchers of the National Security Laboratory of the National Centre for Public Health. Based on their results, the corona-shaped spikes covering the surface of the virus are extremely flexible, the virus has the ability to self-heal and may be one of the most resilient biological organisms known to humanity. Their study proves that the coronavirus can easily be compressed but restores its shape like a rubber ball and its structure is not damaged by physical impact. All these could greatly contribute to its unusually high infectivity.

A huge amount of knowledge has been gathered about the novel coronavirus (SARS-CoV-2) in the past half year, however there is still a lot of uncertainty regarding its function and properties. The study of Semmelweis University’s researchers has got us one step closer to the understanding of the virus. The research group, led by Dr. Miklós Kellermayer, Dean of the Faculty of Medicine, examined the structure of the coronavirus in collaboration with the researchers of the National Security Laboratory of the National Centre for Public Health. The surface of SARS-COV-2 particles was scanned with the application of atomic force microscopy. In their paper they described the corona-shaped layer of spikes as extremely flexible and showed that the organism itself is also particularly resilient: it can be easily compressed but it easily restores its original shape while its structure and properties are not damaged by physical impact. According to Dr. Miklós Kellermayer, the mechanical and self-healing properties of the virus may enable its adaption to a wide range of environmental conditions and may also contribute to its unusually high infectivity.

The study of Semmelweis University’s researchers is unique because all the publications on the virus released so far have been based on research done on inactivated, chemically treated or frozen samples. The research group led by Dr. Miklós Kellermayer studied active and infectious coronavirus, which was made possible by the application of atomic force microscopy (AFM) following a protocol developed for this specific measurement. The microscope is used to study the topography and nanomechanical properties of atoms, molecules and cells. The method was developed by Gerd Binning and Heinrich Rohrer, earning them the Nobel-prize in 1986. The AFM is the only device capable of taking high resolution images of native pathogens as the sample does not need freezing or fixation, like it does in electron microscopy.

To explore the mechanical properties of SARS-CoV-2, the researchers applied indentation on a particle of the width of about 80 nanometres by the tip of the cantilever. The tip was inserted from the top of the virion to its bottom. The mechanical force compressed the particle, and it regained its original shape after retracting the cantilever. The indentation-retraction process was carried out 100 times on the same particle and the virus remained almost completely intact. This seems to support the hypothesis that SARS-CoV-2 may be one of the physically most resilient and resistant viruses known to humanity.

The researchers of Semmelweis University and the National Security Laboratory of the National Centre for Public Health examined other properties of the structure of the virus. Viruses usually become vulnerable when leaving the host, however SARS-CoV-2 is able to maintain its infectivity for a long time on the surface of objects. The study suggests that the flexibility of the spikes covering the particle may contribute to this characteristic. The results of previous studies differed in the number of corona-shaped spikes covering the outer surface of the virus: according to the study of the University of Cambridge, there are about 24 spikes, while the Max Planck Institute in Germany estimated it around 40. The virion studied by the Hungarian research group had 61 spikes. According to Dr. Miklós Kellermayer this may also prove that the resilience of the viral structure may be higher than previously believed.

In their study, the protein making up the spikes was physically examined as well. Upon the physical force of the needle the corona-shaped spikes started to vibrate at such a high frequency that the AFM, capable of taking 300 images per second was able to capture only a blurry image. Dr. Kellermayer and colleagues suspect that the rapid spike motion enables the virus to carry out an efficient search of target host cell surfaces and connect with them.

The thermal stability of SARS-CoV-2 was also tested: following a heat treatment at 90 Celsius degrees for 10 minutes, the general appearance of the virus was only slightly altered, it has lost some spikes, but remained structurally intact. This may also explain, why it maintained its infectivity in warm-climate countries or despite the summer weather.

Ádám Szabó
Photo: Zoltán Tuba
Illustration: BioRxiv
Translation: Ágnes Raubinek