Irina A. Bakhno

In this study, we constructed plasmids to increase the overall expression level of the SARS-CoV-2 S-protein and its presentation on the cell surface. To this end, we designed a series of plasmid constructs encoding the SARS-CoV-2 S-protein with modifications to its cytoplasmic domain and containing various 5′ and 3′ untranslated regions. Our results confirmed the critical role of the S-protein cytoplasmic domain in limiting its localization to the cell surface. We confirmed that deletion of the 19 C-terminal amino acids, which contain an endoplasmic reticulum retrieval signal, significantly increased S-protein presentation on the cell surface. Furthermore, introducing the HuR-binding site from the CD47 3′ untranslated region and replacing the 19 C-terminal amino acids of the S-protein with the CD47 cytoplasmic tail significantly enhanced total S-protein expression compared to the wild-type S-protein and constructs with the 19-amino-acid deletion. Unfortunately, for the plasmid constructs bearing CD47 elements, their higher surface expression compared to the wild-type S-protein correlated with a high total protein expression level.

Spontaneous sorption of proteins on the nanoparticles’ surface leads to the fact that nanoparticles in biological media are always enveloped by a layer of proteins—the protein corona. Corona proteins affect the properties of nanoparticles and their behavior in a biological environment. In this regard, knowledge about the composition of the corona is a necessary element for the development of nanomedicine. Because proteins have different sorption efficacy, isolating particles with a full corona and characterizing the full corona is challenging. In this study, we propose a photo-activated cross-linker for full protein corona fixation. We believe that the application of our proposed approach will make it possible to capture and visualize the full corona on nanoparticles coated with a lipid shell.