Self-assembly and immunogenicity of virus-like particles from goose astrovirus 1 structural protein following proteolytic maturation in a baculovirus system.

Goose astrovirus 1 (GAstV-1) is a significant pathogen responsible for enteritis and visceral gout in goslings, yet no commercial vaccine is currently available. The difficulty in efficiently culturing the virus in vitro has hindered the development of traditional vaccines. Virus-like particles (VLPs), which lack genetic material and mimic native viral conformation, represent a promising vaccine strategy. In this study, the full-length ORF2 structural protein of GAstV-1 was efficiently expressed using a baculovirus/insect cell system. Maximum expression was observed at an MOI of 5 and 5 days post-infection in both extracellular and intracellular fractions. Western blot analysis indicated that ORF2 undergoes proteolytic cleavage, producing mature proteins of 40/43 kDa core and 25/27 kDa spike fragments. Transmission electron microscopy of ultrathin sections revealed abundant VLPs associated with cytoplasmic membranes, and negatively stained purified VLPs showed typical particles of approximately 30 nm accompanied by 10 nm ring-like structures. Immunization of goslings with as little as 5 μg VLPs induced high levels of specific antibodies and a mixed Th1/Th2 immune response. Following challenge, viral shedding was significantly suppressed in immunized groups, with protection comparable to an inactivated virus vaccine. This work establishes a robust platform for GAstV-1 VLP production, provides new insights into proteolytic processing of the viral structural protein, and demonstrates the strong immunogenicity and protective efficacy of VLPs, supporting their potential as a subunit vaccine against GAstV-1.