Borna disease virus phosphoprotein triggers the organization of viral inclusion bodies by liquid-liquid phase separation

• Published in: International journal of biological macromolecules Vol. 192; pp. 55 - 63
• Main Authors: Hirai, Yuya, Tomonaga, Keizo, Horie, Masayuki
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2021
• Subjects: Animals; Biomolecular condensates; Biomolecular Condensates - metabolism; Biomolecular Condensates - pathology; Borna Disease - metabolism; Borna Disease - pathology; Borna Disease - virology; Borna disease virus; Borna disease virus - physiology; Cell Fractionation - methods; cell nucleus; Cells, Cultured; chronic diseases; Fluorescent Antibody Technique; Inclusion Bodies, Viral - metabolism; Inclusion Bodies, Viral - pathology; Intrinsically disordered regions; Liquid droplets; Liquid-Liquid Extraction; Liquid-liquid phase separation; liquids; Membraneless organelles; Microscopy, Confocal; Mononegavirus; Non-segmented negative-strand RNA viruses; Nucleoprotein; nucleoproteins; Nucleus; Phosphoprotein; phosphoproteins; Phosphoproteins - metabolism; RNA; separation; Viral Proteins - metabolism; Nucleus; Liquid droplets; Borna disease virus; Non-segmented negative-strand RNA viruses; Intrinsically disordered regions; Membraneless organelles; Nucleoprotein; Mononegavirus; Phosphoprotein; Liquid-liquid phase separation; Biomolecular condensates
• ISSN: 0141-8130; 1879-0003; 1879-0003
• DOI: 10.1016/j.ijbiomac.2021.09.153

Inclusion bodies (IBs) are characteristic biomolecular condensates organized by the non-segmented negative-strand RNA viruses belonging to the order Mononegavirales. Although recent studies have revealed the characteristics of IBs formed by cytoplasmic mononegaviruses, that of Borna disease virus 1 (BoDV-1), a unique mononegavirus that forms IBs in the cell nucleus and establishes persistent infection remains elusive. Here, we characterize the IBs of BoDV-1 in terms of liquid-liquid phase separation (LLPS). The BoDV-1 phosphoprotein (P) alone induces LLPS and the nucleoprotein (N) is incorporated into the P droplets in vitro. In contrast, co-expression of N and P is required for the formation of IB-like structure in cells. Furthermore, while BoDV-1 P binds to RNA, an excess amount of RNA dissolves the liquid droplets formed by N and P in vitro. Notably, the intrinsically disordered N-terminal region of BoDV-1 P is essential to drive LLPS and to bind to RNA, suggesting that both abilities could compete with one another. These features are unique among mononegaviruses, and thus this study will contribute to a deeper understanding of LLPS-driven organization and RNA-mediated regulation of biomolecular condensates.