Recombinant Coronavirus Spike (S) Protein Trimer Nanoparticles

Background

The coronavirus spike (S) protein is a surface glycoprotein forming a trimer that mediates viral attachment and membrane fusion. The S protein consists of two main parts called S1 and S2 subunits. The S1 subunit has a segment that detects mammalian cellular receptors (receptor-binding domain, RBD) and is responsible for binding the viral particle to the host cell, while the S2 subunit has transmembrane domains that hold the protein like a rod into the viral membrane. Displaying the prefusion S trimer on nanoparticle scaffolds enables multivalent antigen presentation that more closely mimics the native virus surface. These S trimer nanoparticles are being explored as more potent immunogens, improved platforms for neutralizing antibody screening, and more sensitive diagnostic reagents in animal coronavirus (e.g. porcine, avian, feline) research.

Fig. 1 Schematics of MERS-CoV nanoparticle immunogen assembly

Challenges in Producing Recombinant S Protein Trimer Nanoparticles

Engineering S trimer nanoparticles introduces additional complexity beyond soluble S trimers. Stabilizing the prefusion conformation is critical: without carefully designed mutations, S may drift to postfusion conformations or partially unravel, reducing antigenicity. The fusion of S ectodomains to nanoparticle scaffolds requires optimally designed linkers and orientation to avoid steric hindrance and maintain epitope accessibility. Glycosylation remains a challenge, as heterogeneous N-linked glycans can interfere with particle assembly or epitope presentation. Moreover, ensuring precise stoichiometry and avoiding incomplete decoration of nanoparticles is essential to guarantee uniform antigen display; misassembly or aggregation can complicate purification and reduce immunogenic consistency.

Recombinant Coronavirus S Trimer Nanoparticles at Creative Diagnostics

We have successfully developed several animal coronavirus S trimer nanoparticle expressed in CHO cells. Representative viruses include PEDV (Porcine Epidemic Diarrhea Virus), IBV (Infectious Bronchitis Virus), and FIPV (Feline Infectious Peritonitis Virus).

These nanoparticles present S trimers in a multivalent format and retain the prefusion conformation with typical titers in the 3–6 g/L range. Our platform leverages S-trimer scaffolding into nanoparticles, combining the advantages of native trimer structure and multivalent display for enhanced immunogenicity and assay performance.

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