Characterization of virus-like particles produced by the expression of rotavirus capsid proteins in insect cells

Rotaviruses are triple-layered particles that contain four major capsid proteins, VP2, VP4, VP6, and VP7, and two minor proteins, VP1 and VP3. We have cloned each of the rotavirus genes coding for a major capsid protein into the baculovirus expression system and expressed each protein in insect cells. Coexpression of different combinations of the rotavirus major structural proteins resulted in the formation of stable virus-like particles (VLPs). The coexpression of VP2 and VP6 alone or with VP4 resulted in the production of VP2/6 or VP2/4/6 VLPs, which were similar to double-layered rotavirus particles. Coexpression of VP2, VP6, and VP7, with or without VP4, produced triple-layered VP2/6/7 or VP2/4/6/7 VLPs, which were similar to native infectious rotavirus particles. The VLPs maintained the structural and functional characteristics of native particles, as determined by electron microscopic examination of the particles, the presence of nonneutralizing and neutralizing epitopes on VP4 and VP7, and hemagglutination activity of the VP2/4/6/7 VLPs. The production of VP2/4/6 particles indicated that VP4 interacts with VP6. Cell binding assays performed with each of the VLPs indicated that VP4 is the viral attachment protein. Chimeric particles containing VP7 from two different G serotypes also were obtained. The ability to express individual proteins or to coexpress different subsets of proteins provides a system with which to examine the interactions of the rotavirus structural proteins, the role of individual proteins in virus morphogenesis, and the feasibility of a subunit vaccine.