The impact of mutation sets in receptor-binding domain of SARS-CoV-2 variants on the stability of RBD-ACE2 complex.

Aim: Bioinformatic analysis of mutation sets in receptor-binding domain (RBD) of currently and previously circulating SARS-CoV-2 variants of concern (VOCs) and interest (VOIs) to assess their ability to bind the ACE2 receptor. Methods: In silico sequence and structure-oriented approaches were used to evaluate the impact of single and multiple mutations. Results: Mutations detected in VOCs and VOIs led to the reduction of binding free energy of the RBD-ACE2 complex, forming additional chemical bonds with ACE2, and to an increase of RBD-ACE2 complex stability. Conclusion: Mutation sets characteristic of SARS-CoV-2 variants have complex effects on the ACE2 receptor-binding affinity associated with amino acid interactions at mutation sites, as well as on the acquisition of other viral adaptive advantages.

The increase in the infectious potential of SARS-CoV-2 variants (Alpha, Beta, Gamma, Delta, Omicron, etc.) that causes COVID-19 is mainly due to virus mutations. Particularly important for the development of the disease is the interaction of the coronavirus spike protein with a receptor on the surface of human cell, as a result of which the virus penetrates the cell. Angiotensin-binding enzyme (ACE2) is such a receptor in humans, and there is a receptor-binding domain (RBD) in the coronavirus spike protein. In this study, using bioinformatic methods, an analysis of mutations in the RBD of the virus was carried out to find out their influence on the functionality and ability of the virus to interact with the ACE2 receptor with high stability, which ultimately leads to infection. A number of mutations increase the infectious potential of the virus. More recent variants of the virus have more than one mutation in the RBD, so their effects are complex. It is important that the coronavirus is constantly evolving, increasing the ability to bind to the ACE2 receptor, as well as avoiding the immune response. The Omicron variant, which has at least 15 mutations in the RBD, is the most successful in these directions.

Structural bases for the higher adherence to ACE2 conferred by the SARS-CoV-2 spike Q498Y substitution.

A remarkable number of SARS-CoV-2 variants and other as yet unmonitored lineages harbor amino-acid substitutions with the potential to modulate the interface between the spike receptor-binding domain (RBD) and its receptor ACE2. The naturally occurring Q498Y substitution, which is present in currently circulating SARS-CoV-2 variants, has drawn the attention of several investigations. While computational predictions and in vitro binding studies suggest that Q498Y increases the binding affinity of the spike protein for ACE2, experimental in vivo models of infection have shown that a triple mutant carrying the Q498Y replacement is fatal in mice. To accurately characterize the binding kinetics of the RBD Q498Y-ACE2 interaction, biolayer interferometry analyses were performed. A significant enhancement of the RBD-ACE2 binding affinity relative to a reference SARS-CoV-2 variant of concern carrying three simultaneous replacements was observed. In addition, the RBD Q498Y mutant bound to ACE2 was crystallized. Compared with the structure of its wild-type counterpart, the RBD Q498Y-ACE2 complex reveals the conservation of major hydrogen-bond interactions and a more populated, nonpolar set of contacts mediated by the bulky side chain of Tyr498 that collectively lead to this increase in binding affinity. In summary, these studies contribute to a deeper understanding of the impact of a relevant mutation present in currently circulating SARS-CoV-2 variants which might lead to stronger host-pathogen interactions.

Effect of Delta and Omicron Mutations on the RBD-SD1 Domain of the Spike Protein in SARS-CoV-2 and the Omicron Mutations on RBD-ACE2 Interface Complex.

The receptor-binding domain (RBD) is the essential part in the Spike-protein (S-protein) of SARS-CoV-2 virus that directly binds to the human ACE2 receptor, making it a key target for many vaccines and therapies. Therefore, any mutations at this domain could affect the efficacy of these treatments as well as the viral-cell entry mechanism. We introduce ab initio DFT-based computational study that mainly focuses on two parts: (1) Mutations effects of both Delta and Omicron variants in the RBD-SD1 domain. (2) Impact of Omicron RBD mutations on the structure and properties of the RBD-ACE2 interface system. The in-depth analysis is based on the novel concept of amino acid-amino acid bond pair units (AABPU) that reveal the differences between the Delta and/or Omicron mutations and its corresponding wild-type strain in terms of the role played by non-local amino acid interactions, their 3D shapes and sizes, as well as contribution to hydrogen bonding and partial charge distributions. Our results also show that the interaction of Omicron RBD with ACE2 significantly increased its bonding between amino acids at the interface providing information on the implications of penetration of S-protein into ACE2, and thus offering a possible explanation for its high infectivity. Our findings enable us to present, in more conspicuous atomic level detail, the effect of specific mutations that may help in predicting and/or mitigating the next variant of concern.