Open and closed forms of assembled henipavirus nucleoprotein suggest structural basis of genome access

Henipaviruses, such as Nipah virus, can cause deadly illness and constitute WHO blueprint priorities due to their pandemic potential. Their genomes are packaged within a nucleocapsid consisting of viral nucleoproteins (N). Currently, it is unclear how the encapsidated genome is released from N to allow the viral polymerase to read its sequence. Here, we present the first high-resolution cryo-EM structure of a helical N-RNA filament from Langya henipavirus (LayV), allowing us to identify vertical interactions crucial for assembly. We show that assembly efficiency is sequence-dependent and prefers 5-prime genomic sequences. Further, we solve the structure of an RNA-free assembly of LayV N. Structural comparison of the RNA-bound and RNA-free LayV N shows a conformational opening and closing, even within the assembled state. Our data suggest that N within nucleocapsids may undergo local conformational changes, switching between closed and open states, to temporarily allow access to the encapsidated RNA without nucleocapsid disruption.