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Title: Optimized production and fluorescent labeling of SARS-CoV-2 virus-like particles

SARS-CoV-2 is an RNA enveloped virus responsible for the COVID-19 pandemic that conducted in 6 million deaths worldwide so far. SARS-CoV-2 particles are mainly composed of the 4 main structural proteins M, N, E and S to form 100 nm diameter viral particles. Based on productive assays, we propose an optimal transfected plasmid ratio mimicking the viral RNA ratio in infected cells. This allows SARS-CoV-2 Virus-Like Particle (VLPs) formation composed of the viral structural proteins M, N, E and mature S. Furthermore, fluorescent or photoconvertible VLPs were generated by adding a fluorescent protein tag on N or M mixing with unlabeled viral proteins and characterized by western blots, atomic force microscopy coupled to fluorescence and immuno-spotting. Thanks to live fluorescence and super-resolution microscopies, we quantified VLPs size and concentration. SARS-CoV-2 VLPs present a diameter of 110 and 140 nm respectively for MNE-VLPs and MNES-VLPs with a concentration of 10e12 VLP/ml. In this condition, we were able to establish the incorporation of the Spike in the fluorescent VLPs. Finally, the Spike functionality was assessed by monitoring fluorescent MNES-VLPs docking and internalization in human pulmonary cells expressing or not the receptor hACE2. Results show a preferential maturation of S on N(GFP) labeled VLPs more » and an hACE2-dependent VLP internalization and a potential fusion in host cells. This work provides new insights on the use of non-fluorescent and fluorescent VLPs to study and visualize the SARS-CoV-2 viral life cycle in a safe environment (BSL-2 instead of BSL-3). Moreover, optimized SARS-CoV-2 VLP production can be further adapted to vaccine design strategies.

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Award ID(s):
2026657 2102948
Publication Date:
Journal Name:
Scientific Reports
Nature Publishing Group
Sponsoring Org:
National Science Foundation
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  1. Abstract

    SARS-CoV-2 virus is the causative agent of COVID-19. Here we demonstrate that non-infectious SARS-CoV-2 virus like particles (VLPs) can be assembled by co-expressing the viral proteins S, M and E in mammalian cells. The assembled SARS-CoV-2 VLPs possess S protein spikes on particle exterior, making them ideal for vaccine development. The particles range in shape from spherical to elongated with a characteristic size of 129 ± 32 nm. We further show that SARS-CoV-2 VLPs dried in ambient conditions can retain their structural integrity upon repeated scans with Atomic Force Microscopy up to a peak force of 1 nN.

  2. Severe Acute respiratory syndrome coronavirus (SARS-CoV-1) attaches to the host cell surface to initiate the interaction between the receptor-binding domain (RBD) of its spike glycoprotein (S) and the human Angiotensin-converting enzyme (hACE2) receptor. SARS-CoV-1 mutates frequently because of its RNA genome, which challenges the antiviral development. Here, we per-formed computational saturation mutagenesis of the S protein of SARS-CoV-1 to identify the residues crucial for its functions. We used the structure-based energy calculations to analyze the effects of the missense mutations on the SARS-CoV-1 S stability and the binding affinity with hACE2. The sequence and structure alignment showed similarities between the S proteins of SARS-CoV-1 and SARS-CoV-2. Interestingly, we found that target mutations of S protein amino acids generate similar effects on their stabilities between SARS-CoV-1 and SARS-CoV-2. For example, G839W of SARS-CoV-1 corresponds to G857W of SARS-CoV-2, which decrease the stability of their S glycoproteins. The viral mutation analysis of the two different SARS-CoV-1 isolates showed that mutations, T487S and L472P, weakened the S-hACE2 binding of the 2003–2004 SARS-CoV-1 isolate. In addition, the mutations of L472P and F360S destabilized the 2003–2004 viral isolate. We further predicted that many mutations on N-linked glycosylation sites would increase the stability of the Smore »glycoprotein. Our results can be of therapeutic importance in the design of antivirals or vaccines against SARS-CoV-1 and SARS-CoV-2.« less
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