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In the 2019 pandemic coronavirus outbreak (COVID-19), much research has focused on the role of neutralizing antibodies in combating infection with the acute acute coronavirus-2 respiratory syndrome (SARS). -CoV-2). Most of these studies have been based on genome sequencing, showing matches between the Hypervariable Region (HVR) and the antigen receptor binding (RBD) domain. The results have been difficult to explain, however, due to many factors, such as the rapid decay of antibody titers, as well as the antigenic sequences shared by many other viruses such as the earlier SARS (89% strains of co shared) and flu viruses.
_-_1200_width.jpg?resize=560%2C420&ssl=1 "Study: Binding strength and hydrogen bond numbers between Covid-19 RBD and HVR of antibody. Image credit: NIAID / Flickr")
Study details
A new introduction to the bioRxiv * server describes the interactions between the binding spike protein of the SARS-CoV-2 virus with the antibodies. Earlier studies have addressed the similarities in 3D structures of the spike protein in the two SARS viruses as seen on cryo-EM. When amino acid sequences of spike proteins of the two viruses were compared, they showed a similarity of 77%. Since this does not show the differences in binding, or the effect of temperature and other factors, or the nature of the bond, these studies had not been too successful.
The present study compared the binding strength of the SARS-CoV-2 and SARS-CoV spike protein-antibody centers. Because it is thought to have viral interactions with its angiotensin-converting enzyme receptor 2 (ACE2) or its IgM / IgG antibodies through hydrogen bonding between carboxyl and amino groups, the researchers attempted spectroscopy under use red (FTIR) to understand the nature of bonding as well as the number of bonds. This would help to estimate the severity of a viral attack.
Abnormal temperature dependence
Surprisingly, they found almost identical numbers of bands for either virus at room temperature, or below 27 ° C. In other words, nonspecific antibody reactivity was observed, with the error less than 95%. When the binding occurred at human body temperature, that is, at 37 ° C, or above 31 ° C, antibody specificity improved according to the number of hydrogen bonds available, at 19 and 12, respectively. leth.
This was due to the expansion in the square structure of the protein at higher temperatures. Thermal disruption leads to thermal breakdown of the van der Waals bonds between the protein strands, which reduces the number of such bonds. As a result more hydrogen binding sites became visible.
FTIR showed a similar uptake at 1550 cm-1 for all mixtures, of SARS-CoV-2 spike protein / SARS-CoV-2 antibody and SARS-CoV-2 112 spike protein / SARS-CoV-1 antibody, at 0.5% and 0.4%, respectively. In other words, the bonds between the antibodies and the spike proteins did not become stronger, but instead, a greater number of bonds were formed at higher temperatures. This accounts for the higher specificity, since the higher ratio of bonds leads to effective inhibition of binding for nonspecific antibodies.
These results agree with recently published research that confirms the number of hydrogen bonds in these two virus-antibody sites by following amino acids and by comparing the chains. heavy of antibody molecules targeting both viruses.
![Comparison of the order of antibody 2 and antibody 1 amino acid in terms of the binding difference to the S protein. The IgM was plotted with the blue ribbon in the middle, and the S proteins were represented by the screw ribbons in the protein. top and bottom, where some remnants of a representative epitope in the S. protein were identified. The sequence of antibodies was obtained from the literature [32,33]. Both antibodies form only 2+ hydrogen bonds at room temperature as a result of a folded protein structure, while that number would rise to 19 and 12, respectively, at body temperature. person. As can be measured by the Arrhenius equation, approximately 5% of the S protein would bind to antibody 1 at room temperature, resulting in an inevitable test error that could only be eliminated at body temperature.](https://i0.wp.com/d2jx2rerrg6sh3.cloudfront.net/image-handler/picture/2020/12/2020.12.21.423787v1_-_1200_width.jpg?resize=560%2C905&ssl=1 "Comparison of the order of antibody 2 and antibody 1 amino acid with respect to the binding difference to the S protein. The IgM was plotted with the blue ribbon in the middle, and the S proteins were represented by the screw ribbons in the top and bottom, where some remnants of a representative epitope in the S. protein were identified. A series of antibodies was obtained from the literature [32,33]. Both antibodies form only 2+ hydrogen bonds at room temperature as a result of a folded protein structure, while that number would rise to 19 and 12, respectively, at body temperature. person. As can be measured by the Arrhenius equation, approximately 5% of the S protein would bind to antibody 1 at room temperature, resulting in an inevitable test error that could only be eliminated at body temperature.")
Comparison of the order of antibody 2 and antibody 1 amino acid in terms of the binding difference to the S protein. The IgM was plotted with the blue ribbon in the middle, and the S proteins were represented by the screw ribbons in the protein. top and bottom, where some remnants of a representative epitope in the S. protein were identified. A series of antibodies was obtained from the literature [32,33]. Both antibodies form only 2+ hydrogen bonds at room temperature as a result of a folded protein structure, while that number would rise to 19 and 12, respectively, at body temperature. person. As can be worked out with the Arrhenius equation, about 5% of protein S would bind to antibody 1 at room temperature, resulting in the inevitable error of an irreversible test. but at body temperature.
What is the impact?
Despite the close phylogenetic linkage and very similar sequences found in SARS-CoV and SARS-CoV-2, infrared spectroscopy showed that there were different numbers of hydrogen bonds between the spikes and individual antibody molecules. They found an increase in temperature-dependent binding strength, possibly due to the square structure of protein growth. This was found due to an increase in binding sites, and thus in the number of hydrogen bonds between carboxyl and amino amino acids of the various proteins.
Their results were supported by the absorbent determinations at 37 ° C, when the number of hydrogen bonds of the two antibody types, to SARS-CoV-2 and SARS-CoV respectively, was detected at 19 vs. 11. At 27 ° C, the binding ratio is measured by thermodynamic disorders around 20: 1, describing the non-specificity and binding affinity at the lowest temperature. Information like this will help to estimate the accuracy of the Covid-19 IgM / IgG rapid antibody tests, which are intended to help with faster and more extensive monitoring of vaccine responses, and monitoring on the virus in general.
There is no doubt that our results call for the need to determine human body temperature in future antibody diagnoses, especially when the potential vaccines are being detected, as the binding compound, or SARS-CoV-2 IgM / IgG specificity, is only available. at warmer temperatures, than at normal lab / room temperatures of 20 ° C – 25 ° C, where most vaccine testing is carried out. ”
* Important message
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or treated as fixed information.