In Vitro Wrapping of Non-Enveloped Viral Capsids with Lipid Bilayers

Abstract

In vitro reconstituted virus-like particles (VLPs) – particles with structure identical to those of virus particles except for containing non-infectious genetic information instead of a viral genome – are promising nanocarriers for delivery of therapeutic cargos. Among the simplest examples are the VLPs formed from the capsid protein (CP) of either Cowpea Chlorotic Mottle Virus (CCMV) or Brome Mosaic Virus (BMV), which form spontaneously from purified components upon mixing CCMV or BMV CP with single-stranded RNA under the right pH and ionic strength conditions. The structure of these VLPs is identical to that of the virus particles, consisting of 180 copies of the CP organized as 12 icosahedrally-symmetric pentamers separated by 20 hexamers. In contrast, most viruses that infect mammalian cells are enveloped by a lipid bilayer filled with transmembrane virally-encoded glycoproteins, and it has not yet proved possible to reconstitute these particles from their purified components. To take advantage of the robustness of unenveloped virus capsids and the biocompatibility of lipid-bilayer-wrapped enveloped viruses, we demonstrate in vitro lipid-bilayer wrapping of intact plant viral (CCMV and BMV) capsids. Lipid compositions are chosen to match the opposite charge of the viral capsid, to promote stable membrane association. Our results provide an important first step toward the wrapping of in vitro reconstituted VLPs containing therapeutic mRNA. These enveloped virus-like particles (eVLPs) combine the stability and scalability of plant virus capsids with the functional advantages of lipid envelopes, advancing their potential as platforms for RNA delivery, vaccine design, and therapeutic nanotechnology.