Delayed by Design: Role of Suboptimal Signal Peptidase Processing of Viral Structural Protein Precursors in Flaviviridae Virus Assembly

The Flaviviridae virus family is classified into four different genera, including flavivirus, hepacivirus, pegivirus, and pestivirus, which cause significant morbidity and mortality in humans and other mammals, including ruminants and pigs. These are enveloped, single-stranded RNA viruses sharing a similar genome organization and replication scheme with certain unique features that differentiate them. All viruses in this family express a single polyprotein that encodes structural and nonstructural proteins at the N- and C-terminal regions, respectively. In general, the host signal peptidase cleaves the structural protein junction sites, while virus-encoded proteases process the nonstructural polyprotein region. It is known that signal peptidase processing is a rapid, co-translational event. Interestingly, certain signal peptidase processing site(s) in different Flaviviridae viral structural protein precursors display suboptimal cleavage kinetics. This review focuses on the recent progress regarding the Flaviviridae virus genus-specific mechanisms to downregulate signal peptidase-mediated processing at particular viral polyprotein junction sites and the role of delayed processing at these sites in infectious virus particle assembly.

Virus-like particles as drug delivery vectors

Virus-like particles (VLPs) assemble spontaneously during the viral cycle or in heterologous systems during expression of viral structural protein. Depending on the complexity of the VLPs, they can be obtained by expression in prokaryotic or eukaryotic expression system from the suitable recombinant vectors, or formed in cell-free conditions. Moreover, they can be built from proteins of a single virus, or can present the proteins or peptides derived from a virus or cell on a platform derived from any other single virus, thus forming chimeric VLPs. VLPs are best known for their immunogenic properties, but the versatility of VLPs allows a wide variety of applications. They are lately in the centre of investigations in vaccinology, drug delivery and gene therapy. This review focuses on utilization of VLPs for drug delivery.

Expression analysis of Bombyx mori parvo-like virus VD2-ORF1 gene encoding a minor structural protein

Bombyx mori parvo-like virus is a small, icosahedral virus containing two single-stranded linear DNA molecules (VD1, VD2). To date, little is known about this virus, how to package. VD2-ORF1 encoded a large viral structural protein with predicted molecular mass of 133 kDa, and this protein was named as P133. It is unusual for 20–22 nm icosahedral viruses to posses so large a structural protein and the function of this protein is still unknown. In this study, the transcription of P133 was examined with quantitative real-time PCR, and the results demonstrated that the mRNA of P133 could be detected from 28 h post inoculation and kept increasing until 72 h post inoculation. P133 C-terminus (P133C) and P133 N-terminus (P133N) were cloned and expressed in E. coli BL21; then the resulting polypeptides were used to produce antibody, respectively. Western blot analysis showed that the protein in virions recognized by anti-P133C and anti-P133N antibody had the same molecular weight, indicating that VD2-ORF1 encoded a viral structural protein without leaky scanning.