Identification of immunogenic determinants of the spike protein of SARS-like coronavirus

Identification of Novel Candidate Epitopes on SARS-CoV-2 Proteins for South America: A Review of HLA Frequencies by Country

Coronavirus disease (COVID-19), caused by the virus SARS-CoV-2, is already responsible for more than 4.3 million confirmed cases and 295,000 deaths worldwide as of May 15, 2020. Ongoing efforts to control the pandemic include the development of peptide-based vaccines and diagnostic tests. In these approaches, HLA allelic diversity plays a crucial role. Despite its importance, current knowledge of HLA allele frequencies in South America is very limited. In this study, we have performed a literature review of datasets reporting HLA frequencies of South American populations, available in scientific literature and/or in the Allele Frequency Net Database. This allowed us to enrich the current scenario with more than 12.8 million data points. As a result, we are presenting updated HLA allelic frequencies based on country, including 91 alleles that were previously thought to have frequencies either under 5% or of an unknown value. Using alleles with an updated frequency of at least ≥5% in any South American country, we predicted epitopes in SARS-CoV-2 proteins using NetMHCpan (I and II) and MHC flurry. Then, the best predicted epitopes (class-I and -II) were selected based on their binding to South American alleles (Coverage Score). Class II predicted epitopes were also filtered based on their three-dimensional exposure. We obtained 14 class-I and four class-II candidate epitopes with experimental evidence (reported in the Immune Epitope Database and Analysis Resource), having good coverage scores for South America. Additionally, we are presenting 13 HLA-I and 30 HLA-II novel candidate epitopes without experimental evidence, including 16 class-II candidates in highly exposed conserved areas of the NTD and RBD regions of the Spike protein. These novel candidates have even better coverage scores for South America than those with experimental evidence. Finally, we show that recent similar studies presenting candidate epitopes also predicted some of our candidates but discarded them in the selection process, resulting in candidates with suboptimal coverage for South America. In conclusion, the candidate epitopes presented provide valuable information for the development of epitope-based strategies against SARS-CoV-2, such as peptide vaccines and diagnostic tests. Additionally, the updated HLA allelic frequencies provide a better representation of South America and may impact different immunogenetic studies.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a newly emerged pathogen: an overview

Coronavirus disease 2019 (COVID-19) is a viral pneumonia, responsible for the recent pandemic, and originated from Wuhan, China, in December 2019. The causative agent of the outbreak was identified as coronavirus and designated as severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2). Few years back, the severe acute respiratory syndrome coronavirus (SARS- CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV) were reported to be highly pathogenic and caused severe infections in humans. In the current situation SARS-CoV-2 has become the third highly pathogenic coronavirus that is responsible for the present outbreak in human population. At the time of this review, there were more than 14 007 791 confirmed COVID-19 patients which associated with over 597 105 deaths in more then 216 countries across the globe (as reported by World Health Organization). In this review we have discussed about SARS-CoV, MERS-CoV and SARC-CoV-2, their reservoirs, role of spike proteins and immunogenicity. We have also covered the diagnosis, therapeutics and vaccine status of SARS-CoV-2.

Analysis of the Genome Sequence and Prediction of B-Cell Epitopes of the Envelope Protein of Middle East Respiratory Syndrome-Coronavirus

The outbreak of Middle East respiratory syndrome-coronavirus (MERS-CoV) in South Korea in April 2015 led to 186 infections and 37 deaths by the end of October 2015. MERS-CoV was isolated from the imported patient in China. The envelope (E) protein, a small structural protein of MERS-CoV, plays an important role in host recognition and infection. To identify the conserved epitopes of the E protein, sequence analysis was performed by comparing the E proteins from 42 MERS-CoV strains that triggered severe pandemics and infected humans in the past. To predict the potential B cell epitopes of E protein, three most effective online epitope prediction programs, the ABCpred, Bepipred, and Protean programs from the LaserGene software were used. All the nucleotides and amino acids sequences were obtained from the NCBI Database. One potential epitope with a suitable length (amino acids 58-82) was confirmed and predicted to be highly antigenic. This epitope had scores of >0.80 in ABCpred and level 0.35 in Bepipred programs. Due to the lack of X-ray crystal structure of the E protein in the PDB database, the simulated 3D structure of the E protein were also predicted using PHYRE 2 and Pymol programs. In conclusion, using bioinformatics methods, we analyzed the genome sequence of MERS-CoV and identified a potential B-cell epitope of the E protein, which might significantly improve our current MERS vaccine development strategies.

Molecular Basis of Coronavirus Virulence and Vaccine Development

Virus vaccines have to be immunogenic, sufficiently stable, safe, and suitable to induce long-lasting immunity. To meet these requirements, vaccine studies need to provide a comprehensive understanding of (i) the protective roles of antiviral B and T-cell-mediated immune responses, (ii) the complexity and plasticity of major viral antigens, and (iii) virus molecular biology and pathogenesis. There are many types of vaccines including subunit vaccines, whole-inactivated virus, vectored, and live-attenuated virus vaccines, each of which featuring specific advantages and limitations. While nonliving virus vaccines have clear advantages in being safe and stable, they may cause side effects and be less efficacious compared to live-attenuated virus vaccines. In most cases, the latter induce long-lasting immunity but they may require special safety measures to prevent reversion to highly virulent viruses following vaccination. The chapter summarizes the recent progress in the development of coronavirus (CoV) vaccines, focusing on two zoonotic CoVs, the severe acute respiratory syndrome CoV (SARS-CoV), and the Middle East respiratory syndrome CoV, both of which cause deadly disease and epidemics in humans. The development of attenuated virus vaccines to combat infections caused by highly pathogenic CoVs was largely based on the identification and characterization of viral virulence proteins that, for example, interfere with the innate and adaptive immune response or are involved in interactions with specific cell types, such as macrophages, dendritic and epithelial cells, and T lymphocytes, thereby modulating antiviral host responses and viral pathogenesis and potentially resulting in deleterious side effects following vaccination.

The identification and characterization of nucleic acid chaperone activity of human enterovirus 71 nonstructural protein 3AB

Human enterovirus 71 (EV71) belongs to the genus Enterovirus in the family Picornaviridae and has been recognized as one of the most important pathogens that cause emerging infectious disease. Despite of the importance of EV71, the nonstructural protein 3AB from this virus is little understood for its function during EV71 replication. Here we expressed EV71 3AB protein as recombinant protein in a eukaryotic expression system and uncovered that this protein possesses a nucleic acid helix-destabilizing and strand annealing acceleration activity in a dose-dependent manner, indicating that EV71 3AB is a nucleic acid chaperone protein. Moreover, we characterized the RNA chaperone activity of EV71 3AB, and revealed that divalent metal ions, such as Mg²⁺ and Zn²⁺, were able to inhibit the RNA helix-destabilizing activity of 3AB to different extents. Moreover, we determined that 3B plus the last 7 amino acids at the C-terminal of 3A (termed 3B+7) possess the RNA chaperone activity, and five amino acids, i.e. Lys-80, Phe-82, Phe-85, Tyr-89, and Arg-103, are critical and probably the active sites of 3AB for its RNA chaperone activity. This report reveals that EV71 3AB displays an RNA chaperone activity, adds a new member to the growing list of virus-encoded RNA chaperones, and provides novel knowledge about the virology of EV71.