A Novel Interaction Reveals LC8 as a Potential Hijacking Point for a Respiratory Virus

Abstract

Lower respiratory tract infections (LRTIs) are a major cause of death among immunocompromised patients. Human parainfluenza viruses (hPIVs) are non‐segmented, negative‐stranded RNA viruses that frequently give rise to these infections. In order to transcribe genes or replicate their genomes, these viruses encode three major genes: a nucleocapsid (N), a phosphoprotein (P) and a large RNA‐dependent RNA polymerase (L). P is indispensable for transcription and replication as it positions L at the replication/transcriptional start site and recruits accessory proteins. Phosphoprotein structure has been characterized in related viruses such as measles and mumps, where P has been shown to be an oligomer, featuring an intrinsically disordered region as well as a flexible multimerization domain. However, P has not been well studied in the hPIVs and its oligomerization state and dynamics remain unclear. In this study, we show that the phosphoprotein of hPIV type 3 (hPIV3‐P) interacts with host ‘hub’ protein LC8 resulting in structural changes. LC8 is known to bind over a hundred different proteins in eukaryotic cells, facilitating a functional structure. LC8 preferentially binds to intrinsically disordered regions within binding partners which ultimately results in self association, support, oligomerization or other structural rearrangements required for proper function. We have identified two conserved potential LC8 binding sites within hPIV3‐P using the LC8Pred algorithm. We recombinantly expressed and purified a construct featuring the coiled coil domain of the protein and the LC8 binding site in closest proximity to it. LC8 binding was confirmed via pulldown assays, isothermal titration calorimetry (ITC) and size exclusion chromatography (SEC). Further, we characterized the stability of the coiled coil domain using circular dichroism spectroscopy (CD) and the oligomerization state of the protein bound and unbound to LC8 using analytical ultracentrifugation (AUC). Our results show a well‐defined novel interaction that might be indispensable for phosphoprotein activity and overall viral viability. This adds to the evidence that LC8 is a common target for viral hijacking due to its structural properties. Support or Funding Information This work is funded by NSF MCB 1617019