Abstract
The baculovirus-insect cell expression system has been widely used for heterologous protein expression and virus-like particles (VLPs) expression. In this study, we established a new method for antiviral screening targeting to glycoprotein E of flaviviruses based on the baculovirus expression system. ZIKV is a mosquito-borne flavivirus and has posed great threat to the public health. It has been reported that ZIKV infection was associated with microcephaly and serious neurological complications. Our study showed that either ZIKV E or prME protein expressed in insect cells can form VLPs and induce membrane fusion between insect cells. Therefore, the E protein, which is responsible for receptor binding, attachment, and virus fusion during viral entry, achieved proper folding and retained its fusogenic ability in VLPs when expressed in this system. The syncytia in insect cells were significantly reduced by the anti-ZIKV-E specific polyclonal antibody in a dose-dependent manner. AMS, a thiol-conjugating reagent, was also shown to have an inhibitory effect on the E protein induced syncytia and inhibited ZIKV infection by blocking viral entry. Indeed the phenomenon of syncytial formation induced by E protein expressed VLPs in insect cells is common among flaviviruses, including Japanese encephalitis virus (JEV), Dengue virus type 2 (DENV-2), and tick-borne encephalitis virus (TBEV). This inhibition effect on syncytial formation can be developed as a novel, safe, and simple antiviral screening approach for inhibitory antibodies, peptides, or small molecules targeting to E protein of ZIKV and other flaviviruses.
Highlights
The baculovirus-insect cell expression system (BES) is one of the most widely used eukaryotic systems for heterologous protein expression and has been used for functional studies, vaccine preparations, and diagnostics
We tested whether the phenomenon of syncytial formation induced by E protein was common for other flaviviruses and we found that syncytia were induced by baculovirus-expressed E protein of Dengue virus type 2 (DENV-2), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV)
This system has been used for virus-like particles (VLPs) production of JEV [16], functional analysis of prM protein of JEV [27], and evaluation of antigenic activity of E protein of Yellow fever virus (YFV) [28]
Summary
The baculovirus-insect cell expression system (BES) is one of the most widely used eukaryotic systems for heterologous protein expression and has been used for functional studies, vaccine preparations, and diagnostics. Upon infection with a recombinant baculovirus carrying the foreign gene of interest, host cells often express the heterologous protein at very high yield and allow eukaryotic-type post-translational modifications (like N- and O-glycosylation, acylation, and phosphorylation) in contrast to prokaryotic expression systems [1]. These advantages make it possible to express proteins that are soluble and conformationally, immunogenically, and functionally. A licensed human papillomavirus-like particle vaccine Cervarix® has been manufactured using this system [4]
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