Mouse Anti-Baculovirus Envelope gp64 protein Monoclonal antibody, clone BdW2

Baculoviruses consist of double-stranded circular DNA viruses that have a membrane envelope and mainly infect invertebrate hosts. They exist mainly in two forms: occlusion-derived virus (ODV) and budding virus (BV). Although both forms possess identical genetic sequences they exhibit differences in their physical shape and structure of their surrounding membrane along with their composition and functionality. Genetic engineering transforms baculoviruses into effective delivery systems for applications in the biopharmaceutical and gene therapy sectors. The Baculovirus Expression Vector (BEV) system enables numerous worldwide pharmaceutical companies to mass-produce recombinant proteins.

The baculovirus expression system (BEVS) operates as a eukaryotic expression system utilized extensively to express foreign target genes and produce vaccines with high titers. Experimental evidence has demonstrated that this expression system provides multiple benefits for producing foreign proteins. The expression products generated by this system achieve correct folding structures and include various post-translational modifications like glycosylation as well as phosphorylation and acylation. This expression system enables the simultaneous expression of many foreign genes along with large DNA fragments. The virus targets only invertebrates while exhibiting excellent biosafety features. Multiple limitations of the baculovirus expression system persist during its practical large-scale application. Production challenges arise within the baculovirus expression system because insect cells generate humanized glycoproteins that undergo structural and functional alterations from substantial N-glycosylation differences compared to mammalian cells. Furthermore, target proteins are prone to degradation by proteases present in insect cells.

GP64 functions as the principal envelope glycoprotein that controls several stages of the viral life cycle through its involvement in host cell attachment, membrane fusion, and viral budding. Autographa californica multiple nucleopolyhedrovirus (AcMNPV) houses the gp64 gene which produces a protein composed of 512 amino acids. The structural domain of the protein holds a signal peptide which functions to target the protein to the cell membrane. GP64 is the main fusion partner in most BEVS surface display technologies. The baculovirus viral glycoprotein GP64 allows the integration of foreign proteins onto the membranes of infected cells. Researchers usually connect foreign proteins like hemagglutinin (HA) from influenza A virus to either the GP64 signal peptide (SP), transmembrane domain (TMD), cytoplasmic tail domain (C-terminal domain, CTD), or both TMD and CTD domains of GP64. In viral vector applications, GP64 can be used for vaccine development. For example, GP64 fused with influenza HA protein can induce a strong neutralizing antibody response.

Figure 1. Schematic of the rod-shaped AcMNPV BV particle
(Source: Tsai CH, et al. 2020)