Structural Description of the Nipah Virus Phosphoprotein and Its Interaction with STAT1

Abstract

The structural characterization of modular proteins containing long intrinsically disordered regions intercalated with folded domains is complicated by their conformational diversity and flexibility and requires the integration of multiple experimental approaches. Nipah virus (NiV) phosphoprotein, an essential component of the viral RNA transcription/replication machine and a component of the viral arsenal that hijacks cellular components and counteracts host immune responses, is a prototypical model for such modular proteins. Curiously, the phosphoprotein of NiV is significantly longer than the corresponding protein of other paramyxoviruses. Here, we combine multiple biophysical methods, including x-ray crystallography, NMR spectroscopy, and small angle x-ray scattering, to characterize the structure of this protein and provide an atomistic representation of the full-length protein in the form of a conformational ensemble. We show that full-length NiV phosphoprotein is tetrameric, and we solve the crystal structure of its tetramerization domain. Using NMR spectroscopy and small angle x-ray scattering, we show that the long N-terminal intrinsically disordered region and the linker connecting the tetramerization domain to the C-terminal X domain exchange between multiple conformations while containing short regions of residual secondary structure. Some of these transient helices are known to interact with partners, whereas others represent putative binding sites for yet unidentified proteins. Finally, using NMR spectroscopy and isothermal titration calorimetry, we map a region of the phosphoprotein, comprising residues between 110 and 140 and common to the V and W proteins, that binds with weak affinity to STAT1 and confirm the involvement of key amino acids of the viral protein in this interaction. This provides new, to our knowledge, insights into how the phosphoprotein and the nonstructural V and W proteins of NiV perform their multiple functions.