SARS-CoV-2 virus-like-particles via liposomal reconstitution of spike glycoproteins.

The SARS-CoV-2 virus, implicated in the COVID-19 pandemic, recognizes and binds host cells using its spike glycoprotein through an angiotensin converting enzyme 2 (ACE-2) receptor-mediated pathway. Recent research suggests that spatial distributions of the spike protein may influence viral interactions with target cells and immune systems. The goal of this study has been to develop a liposome-based virus-like particle (VLP) by reconstituting the SARS-CoV-2 spike glycoprotein within a synthetic nanoparticle membrane, aiming to eventually establish tunability in spike protein presentation on the nanoparticle surface. Here we report on first steps to this goal, wherein liposomal SARS-CoV-2 VLPs were successfully produced via detergent mediated spike protein reconstitution. The resultant VLPs are shown to successfully co-localize in vitro with the ACE-2 receptor on lung epithelial cell surfaces, followed by internalization into these cells. These VLPs are the first step toward the overall goal of this research which is to form an understanding of the relationship between spike protein surface density and cell-level immune response, eventually toward creating better vaccines and anti-viral therapeutics.

Serum proteins on nanoparticles: early stages of the "protein corona".

Nanoparticles in biological systems such as the bloodstream are exposed to a complex solution of biomolecules. A "corona" monolayer of proteins has historically been thought to form on nanoparticles upon introduction into such environments. To examine the first steps of protein binding, Fluorescence Correlation/Cross Correlation Spectroscopy and Fluorescence Resonance Energy Transfer were used to directly analyze four different nanoparticle systems. CdSe/ZnS core/shell quantum dots, 100 nm diameter polystyrene fluospheres, 200 nm diameter polystyrene fluospheres, and 200 nm diameter PEG-grafted DOTAP liposomes were studied with respect to serum protein binding, using bovine serum albumin as a model. Surface heterogeneity is found to be a key factor in protein binding to these nanoparticles, and as such we present a novel conceptualization of the early hard corona as low-ratio, non-uniform binding rather than a uniform monolayer.