Structure and assembly of Borna disease virus 1 nucleoprotein-RNA complexes

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• The nucleoprotein (N) complex is crucial for negative-strand RNA virus replication.
• Structures of Bornaviridae N-RNA complexes were previously unreported.
• Borna disease virus 1 (BoDV-1) is a significant veterinary pathogen.

Purpose of the Study:

• To elucidate the high-resolution structures of BoDV-1 N-RNA complexes.
• To understand the N-RNA engagement mechanism in Bornaviridae.
• To investigate the role of N oligomerization in nucleocapsid assembly.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine N-RNA complex structures.
• Mutational analyses were performed to identify key residues for nucleocapsid formation.
• Structural data were analyzed to understand N-RNA stoichiometry and oligomerization.

Main Results:

• High-resolution structures revealed dominant hexameric, heptameric, and octameric N-RNA complexes.
• A BoDV-1 specific stoichiometry of eight nucleotides per N was determined.
• Multiple RNA-free N oligomers were identified, indicating conformational flexibility.
• Mutational studies identified residues critical for nucleocapsid formation and RNA synthesis.
• Cryo-EM of mutant complexes suggested N oligomerization precedes RNA binding.

Conclusions:

• The study provides the first structural insights into Bornaviridae N-RNA complexes.
• BoDV-1 N-RNA structures reveal unique features and stoichiometry.
• Conformational plasticity of N contributes to nucleocapsid assembly.
• Findings offer a framework for comparative studies with other negative-strand RNA viruses.