Co-expression of Four Major Structural Proteins of Bluetongue Virus Can Assemble into Virus-like Particles
In order to develop novel genetically engineered vaccine for bluetongue virus (BTV) and study the relationship between structure and function of BTV proteins, the assembly of virus-like particles of BTV was conducted in this paper. The four major structural proteins of BTV, VP3, VP7, VP2 and VP5, were expressed simultaneously in insect cells. After purification, two kinds of particles could be found: one was similar to the core-like particles (CLPs) (diameter in 60-70nm, the thickness of the capsid is about 10-15nm) as described before, another was just like empty intact BTV virions (diameter in 70-80nm, the thickness of the capsid was about 20-30nm). Further analysis showed that the expressed particles contain VP2/VP3, VP5 and VP7, but no other BTV proteins or any nucleic acids were found. The expressed particles could elicit neutralizing antibodies and showed hemagglutination activities. It indicated that the four structural proteins could be assembled into virus like particles, though the effectiveness of assembly was relatively low than that of CLPs. The results also implied that the domains related to the assembly of BTV VLPs may be conserved, the interaction between the inner and outer capsid proteins and the initiation of the assembly had nothing to do with the high variation region of VP2.