Crystal structure of the Borna disease virus nucleoprotein

Borna disease virus (BDV) causes an infection of the central nervous system in a wide range of vertebrates, which can fatally progress to an immune-mediated disease, called Borna disease. BDV is a member of the Mononegavirales, which also includes the highly infectious measles and Ebola viruses. The viral nucleo-proteins are central to transcription, replication, and packaging of the RNA genome. We present the X-ray structure of the BDV nucleoprotein determined at 1.76 Angstrom resolution. The structure reveals a novel fold, organized into two distinct domains, and an assembly into a planar homotetramer. Surface potential calculations strongly support an RNA binding model with the RNA wrapping around the outside of the tetramer, although a positively charged central channel in the tetramer could fit single-stranded RNA in an alternative binding mode. This first structure of an RNA virus nucleoprotein provides a paradigmatic model for RNA packaging and replication of single-stranded RNA viruses.