Viral surface geometry shapes influenza and coronavirus spike evolution through antibody pressure

The Immunological Basis for Vaccination

Vaccination is crucial for health protection of poultry and therefore important to maintaining high production standards. Proper vaccination requires knowledge of the key players of the well-orchestrated immune system of birds, their interdependence and delicate regulation, and, subsequently, possible modes of stimulation through vaccine antigens and adjuvants. The knowledge about the innate and acquired immune systems of birds has increased significantly during the recent years but open questions remain and have to be elucidated further. Despite similarities between avian and mammalian species in their composition of immune cells and modes of activation, important differences exist, including differences in the innate, but also humoral and cell-mediated immunity with respect to, for example, signaling transduction pathways, antigen presentation, and cell repertoires. For a successful vaccination strategy in birds it always has to be considered that genotype and age of the birds at the time point of immunization as well as their microbiota composition may have an impact and may drive the immune reactions into different directions. Recent achievements in the understanding of the concept of trained immunity will contribute to the advancement of current vaccine types helping to improve protection beyond the specificity of an antigen-driven immune response. The fast developments in new omics technologies will provide insights into protective B- and T-cell epitopes involved in cross-protection, which subsequently will lead to the improvement of vaccine efficacy in poultry.

Understanding the role of conserved proline and serine residues in the SARS-CoV-2 spike cleavage sites in the virus entry, fusion, and infectivity

The spike (S) glycoprotein of the SARS-CoV-2 virus binds to the host cell receptor and promotes the virus's entry into the target host cell. This interaction is primed by host cell proteases like furin and TMPRSS2, which act at the S1/S2 and S2´ cleavage sites, respectively. Both cleavage sites have serine or proline residues flanking either the single or polybasic region and were found to be conserved in coronaviruses. Unravelling the effects of these conserved residues on the virus entry and infectivity might facilitate the development of novel therapeutics. Here, we have investigated the role of the conserved serine and proline residues in the SARS-CoV-2 spike mediated entry, fusogenicity, and viral infectivity by using the HIV-1/spike-based pseudovirus system. A conserved serine residue mutation to alanine (S2´S-A) at the S2´ cleavage site resulted in the complete loss of spike cleavage. Exogenous treatment with trypsin or overexpression of TMPRSS2 protease could not rescue the loss of spike cleavage and biological activity. The S2´S-A mutant showed no significant responses against E-64d, TMPRSS2 or other relevant inhibitors. Taken together, serine at the S2´ site in the spike protein was indispensable for spike protein cleavage and virus infectivity. Thus, novel interventions targeting the conserved serine at the S2´ cleavage site should be explored to reduce severe disease caused by SARS-CoV-2-and novel emerging variants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03749-y.

Effect of Disulfide Bridge on the Binding of SARS-CoV-2 Fusion Peptide to Cell Membrane: A Coarse-Grained Study

In this paper, we present the parameterization of the CAVS coarse-grained (CG) force field for 20 amino acids, and our CG simulations show that the CAVS force field could accurately predict the amino acid tendency of the secondary structure. Then, we used the CAVS force field to investigate the binding of a severe acute respiratory syndrome-associated coronavirus fusion peptide (SARS-CoV-2 FP) to a phospholipid bilayer: a long FP (FP-L) containing 40 amino acids and a short FP (FP-S) containing 26 amino acids. Our CAVS CG simulations displayed that the binding affinity of the FP-L to the bilayer is higher than that of the FP-S. We found that the FP-L interacted more strongly with membrane cholesterol than the FP-S, which should be attributed to the stable helical structure of the FP-L at the C-terminus. In addition, we discovered that the FP-S had one major and two minor membrane-bound states, in agreement with previous all-atom molecular dynamics (MD) studies. However, we found that both the C-terminal and N-terminal amino acid residues of the FP-L can strongly interact with the bilayer membrane. Furthermore, we found that the disulfide bond formed between Cys840 and Cys851 stabilized the helices of the FP-L at the C-terminus, enhancing the interaction between the FP-L and the bilayer membrane. Our work indicates that the stable helical structure is crucial for binding the SARS-CoV-2 FP to cell membranes. In particular, the helical stability of FP should have a significant influence on the FP-membrane binding.

Hydrodynamics of spike proteins dictate a transport-affinity competition for SARS-CoV-2 and other enveloped viruses

Many viruses, such as SARS-CoV-2 or Influenza, possess envelopes decorated with surface proteins (a.k.a. spikes). Depending on the virus type, a large variability is present in the surface-proteins number, morphology and reactivity, which remains generally unexplained. Since viruses' transmissibility depends on features beyond their genetic sequence, new tools are required to discern the effects of spikes functionality, interaction, and morphology. Here, we postulate the relevance of hydrodynamic interactions in the viral infectivity of enveloped viruses and propose micro-rheological characterization as a platform for virus differentiation. To understand how the spikes affect virion mobility and infectivity, we investigate the diffusivity of spike-decorated structures using mesoscopic-hydrodynamic simulations. Furthermore, we explored the interplay between affinity and passive viral transport. Our results revealed that the diffusional mechanism of SARS-CoV-2 is strongly influenced by the size and distribution of its spikes. We propose and validate a universal mechanism to explain the link between optimal virion structure and maximal infectivity for many virus families.