SARS-CoV-2 D614G mutation associated with lower antibody binding

The onset of the 2019 coronavirus pandemic (COVID-19) has made an international effort to find the biology of its causative agent, coronavirus respiratory syndrome 2 (SARS-CoV-2), and to develop effective and safe antivirals to control and treat the disease. A new study by a team of researchers in France and Sweden cites one such study, examining the relative immunogenicity of the three major structural proteins of the virus. The team is on their findings about the bioRxiv * preprint server.

SARS-CoV-2 affects the host cells through its superficial glycoprotein spike. Once viral entry is achieved, it uses the cell’s machinery to translate its RNA genome into structural and non-structural proteins, as well as accessory proteins, ensuring that the structure is high their right-school and tertiary to complete the task.

The main viral proteins include the spike, envelope and organ proteins, all of which are exposed to the immune system. As a result, they stimulate antibody responses, which in turn not only neutralize viral entry into the host cells, but activate other immune pathways leading to its insertion of immune cells and destruction of whole-mediated cells.

Antibodies to S, M and E proteins.

With little information on antibody responses to the M and E proteins, the current study aimed to understand the ability of these two viral proteins, along with the spike antigen, to stimulate antibody production, using a system based on human cells. This platform was designed for viral insertion into the cell membrane and N-glycosylation, as these are considered essential for antibody recognition.

The researchers found that the serological responses showed a similar pattern in all COVID-19 patients, with moderate, moderate, or severe disease. The antibody profiles were comparable to those obtained by diagnostic evaluations, with approximately 90% consistency.

The control serra showed no binding to the proteins S, E or M, so they were used to set the reference for seropositivity.

Both COVID-19 patients and those with COVID-19-like symptoms showed antibodies immunoglobulin G (IgG), IgM and IgA to the spike protein. Patients with moderate to severe infection had higher titers of antibodies to the spike protein than with moderate infection. Severe infection associated with anti-M antibodies was also observed.

Anti-M antibodies were always associated with anti-spike antibodies, but the converse was not true. Anti-E antibodies were not detected in any patients.

The D614G mutation changes the spike structure

The researchers also found that the D614 spike, which was typical of the virus in the previous part of the pandemic, was structurally different from the G614 mutant spike, which indicates the normal variability that is controlling throughout the virus. universe. The earlier version has a salt bridge connecting two spike primers at the remains of D614-K854, as well as between R646 and E865.

With the G614 mutant, the K854 makes a hydrogen bond to the G614 backbone, which is a weaker and more energetic bond. There are changes in the non-polar region of protomer B spike, which goes towards protomer A in the D614 version but is pushed away in the G614 mutant.

The latter has the same electrostatic interactions with the latter with the second interaction. In addition, the part around the K854 position in protomer B is moved around to mark away from protomer A. Increased solution transparency was observed with the pole residues around E685 of protomer B. All all in all, therefore, the G614 mutation alters the structure of the spike protein, which in turn alters the immune response.

D614G mutation reduced antibody spike binding

When the antibodies to the spike antigen were reassessed with sera from COVID-19 patients, using both variants of the spike, they found that the mutation does not reduce the antigenicity of the spike antigen, but instead reduces it. IgG, IgM, and IgA binding to the G614 spike version.

European patients were mostly contaminated with the G614 spike version, rather than the D614 version on which most commercial evaluations are based. Previous study showed no difference in antibody binding, using an ELISA test.

This result indicates that antigens used to study antibody responses should correctly detect the viral proteins.

What is the impact?

Our experimental system allows a distinction between D614 vs G614 Ig anti-S signals that are likely due to the advantage of using Spike inserted after complex and complex modifications and post-translation. “

The study also demonstrates the benefits of using the full-length spike, rather than just the S1 subunit or the receptor binding domain (RBD) alone. The first is done through a proper translational translation, allowing it to acquire structural integrity. This makes it more likely to detect the full range of antibody response.

The researchers showed generation of antibodies against full M protein rather than antigenic peptides, for the first time, confirming earlier evaluations performed with microarrays. Lack of anti-E antibodies may be due to a lack of surface sensitivity of this protein, or a lack of antigenicity. In fact, some research suggests that this protein is found mainly within the protein processing regions of the cell.

Given that strong anti-M Ig responses, and none of the new variants exhibit M mutations, the potential of these antibodies to achieve effective neutralization needs to be investigated. If so, this protein, stored over layers, could be the basis for more stable vaccines.

At the moment, with the vaccination campaigns in many countries going on, at the same time as the release of new changes, the researchers present their serological test as “a reliable trial to determine the efficacy of a vaccine during immunization and to investigate the effect of these Spike mutations on antibody responses. ”

* 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.