A novel fusion protein of COVID-19 virus enhancing protection of Syrian hamsters infected with SARS-CoV-2.

COVID-19 and its variants have spread around the world, triggering a range of long-term sequelae and leading to the need for broadly effective vaccines. We have established a new fusion protein combining the receptor-binding domain region (SF2) and a newly identified conserved binding region (SF5) from the spike of SARS-CoV-2. This fusion protein (COVID19-SF2+SF5) specifically bound to VERO-E6 cells with higher efficiency than either region alone. Antibodies raised in mice against COVID19-SF2+SF5 cross-reacted with every fragment of SARS-CoV-2 and SARS. Additionally, antibodies against the fusion protein effectively neutralize pseudoviruses of both wild-type and mutant strains of SARS-CoV-2 (including BA.3, XBB.1.5, and EG.5), as well as SARS pseudoviruses. Protein interaction prediction and binding affinity determination revealed that the fusion protein exhibits strong binding capacity to three key host molecules: heparan sulfate proteoglycan (HSPG), neuropilin-1 (NRP1), and cluster of differentiation 147 (CD147). Analysis of representative viruses from four coronavirus genera (α, β, γ, δ)-including 229E, NL63, OC43, HKU1, SARS-CoV, MERS-CoV, HKU20, and IBV-revealed that these coronaviruses share sequence similarity mainly on SF2 and SF5 regions. Furthermore, immunization of female hamsters with COVID19-SF2+SF5 provided significant protection against a SARS-CoV-2 virus challenge. Taken together, our results indicate that vaccination with a protein containing both an receptor binding domain (RBD) region and a common binding region provides strong protection during infection, thus suggesting a potential strategy to avoid evasion of host immune recognition by virus variants. Significantly, the observation that COVID19-SF2+SF5 immunization possesses stronger activity in reducing viral load at early stages suggests that the SF5 region might play an important role in virus recognition and binding to host cells. Based on these findings, we conclude that it is possible to develop universal vaccines and neutralizing monoclonal antibodies to curb the effects of mutations and to target multiple coronaviruses.