A single amino acid substitution in the Borna disease virus glycoprotein enhances the infectivity titer of vesicular stomatitis virus pseudotyped virus by altering membrane fusion activity

Abstract

Borna disease virus 1 (BoDV-1) causes acute fatal encephalitis in mammals, including humans. Despite its importance, research on BoDV-1 cell entry has been hindered by low viral particle production in cells and the lack of cytopathic effects. To address these issues, we developed a method to efficiently produce vesicular stomatitis virus (VSV) pseudotyped with glycoprotein (G) of the genus Orthobornavirus, including BoDV-1. We discovered that optimal G expression is required to obtain a high infectivity titer of the VSV pseudotyped virus. Remarkably, the infectivity of the VSV pseudotyped virus with G from the BoDV-1 strain huP2br was significantly higher than that of the VSV pseudotyped virus with G from the He/80 strain. Mutational analysis demonstrated that the BoDV-1-G residue 307 determines the infectivity titer of VSV pseudotyped with BoDV-1-G (VSV-BoDV-1-G). A cell-cell fusion assay indicated that this residue plays a pivotal role in membrane fusion, thus suggesting that high membrane fusion activity and a broad pH range for membrane fusion are crucial for achieving a high infectivity titer of VSV-BoDV-1-G. This finding may be extended to increase the infectivity titer of VSV pseudotyped virus with other orthobornavirus G. Our study also contributes to identifying functional domains of BoDV-1-G and provides insight into G-mediated cell entry.