Molecular dynamics simulations of the delta and omicron SARS-CoV-2 spike - ACE2 complexes reveal distinct changes between both variants.

SARS-CoV-2, the virus causing the COVID-19 pandemic, changes frequently through the appearance of mutations constantly leading to new variants. However, only few variants evolve as dominating and will be considered as "Variants of Concern" (VOCs) by the world health organization (WHO). At the end of 2020 the alpha (B.1.1.7) variant appeared in the United Kingdom and dominated the pandemic situation until mid of 2021 when it was substituted by the delta variant (B.1.617.2) that first appeared in India as predominant. At the end of 2021, SARS-CoV-2 omicron (B.1.1.529) evolved as the dominating variant. Here, we use in silico modeling and molecular dynamics (MD) simulations of the receptor-binding domain of the viral spike protein and the host cell surface receptor ACE2 to analyze and compare the interaction pattern between the wild type, delta and omicron variants. We identified residue 493 in delta (glutamine) and omicron (arginine) with altered binding properties towards ACE2.

Computational decomposition reveals reshaping of the SARS-CoV-2–ACE2 interface among viral variants expressing the N501Y mutation

Abstract Variants of concern of the SARS-CoV-2 virus with an asparagine-to-tyrosine substitution at position 501 (N501Y) in the receptor-binding domain (RBD) show enhanced infectivity compared to wild-type, resulting in an altered pandemic situation in affected areas. These SARS-Cov-2 variants comprise the two Alpha variants (B.1.1.7, United Kingdom and B.1.1.7 with the additional E484K mutation), the Beta variant (B.1.351, South Africa), and the Gamma variant (P.1, Brazil). Understanding the binding modalities between these viral variants and the host cell receptor ACE2 allows to depict changes, but also common motifs of virus?host cell interaction. The trimeric spike protein expressed at the viral surface contains the RBD that forms the molecular interface with ACE2. All the above-mentioned variants carry between one and three amino acid exchanges within the interface-forming region of the RBD, thereby altering the binding interface with ACE2. Using molecular dynamics (MD) simulations and decomposition of intermolecular contacts between the RBD and ACE2, we identified phenylalanine 486, glutamine 498, threonine 500, and tyrosine 505 as important interface-forming residues across viral variants. However, especially the N501Y exchange increased contact formation for this residue and also induced some local conformational changes. Comparing here, the in silico generated B.1.1.7 RBD?ACE2 complex with the now available experimentally solved structure reveals very similar behavior during MD simulation. We demonstrate, how computational methods can help to identify differences in conformation as well as contact formation for newly emerging viral variants. Altogether, we provide extensive data on all N501Y expressing SARS-CoV-2 variants of concern with respect to their interaction with ACE2 and how this induces reshaping of the RBD?ACE2 interface.

Mutations in the B.1.1.7 SARS-CoV-2 Spike Protein Reduce Receptor-Binding Affinity and Induce a Flexible Link to the Fusion Peptide.

The B.1.1.7 variant of the SARS-CoV-2 virus shows enhanced infectiousness over the wild type virus, leading to increasing patient numbers in affected areas. Amino acid exchanges within the SARS-CoV-2 spike protein variant of B.1.1.7 affect inter-monomeric contact sites within the trimer (A570D and D614G) as well as the ACE2-receptor interface region (N501Y), which comprises the receptor-binding domain (RBD) of the spike protein. However, the molecular consequences of mutations within B.1.1.7 on spike protein dynamics and stability or ACE2 binding are largely unknown. Here, molecular dynamics simulations comparing SARS-CoV-2 wild type with the B.1.1.7 variant revealed inter-trimeric contact rearrangements, altering the structural flexibility within the spike protein trimer. Furthermore, we found increased flexibility in direct spatial proximity of the fusion peptide due to salt bridge rearrangements induced by the D614G mutation in B.1.1.7. This study also implies a reduced binding affinity for B.1.1.7 with ACE2, as the N501Y mutation restructures the RBD-ACE2 interface, significantly decreasing the linear interaction energy between the RBD and ACE2. Our results demonstrate how mutations found within B.1.1.7 enlarge the flexibility around the fusion peptide and change the RBD-ACE2 interface. We anticipate our findings to be starting points for in depth biochemical and cell biological analyses of B.1.1.7.