Structural Conservation and Assembly Plasticity of a Divergent Phenuivirus Nucleoprotein

Tick-borne phenuiviruses include a diverse set of emerging pathogens whose nucleoproteins (NPs) package viral RNA despite extensive sequence divergence across lineages. We examined the NP of Tacheng tick virus 2 (TcTV2), a highly divergent member of the genus Uukuvirus. Phylogenetic analysis of an expanded NP dataset supported the placement of TcTV2 within the broader Uukuvirus lineage, and the AlphaFold model predicted a bilobed core with an electropositive groove resembling those of other phenuivirus NPs. Structural comparisons of the predicted model indicated the greatest variation in the peripheral regions. Recombinant TcTV2 NP co-purified with bacterial RNA and formed heterogeneous ring-like particles, with pentamer-like particles predominating in cryo-EM 2D classes. Truncation of the distal N-terminal region (NP_152-440) did not abolish ring-like particle formation under the tested conditions. Suramin altered the thermal denaturation profile of TcTV2 NP and produced concentration-dependent responses on an NP-loaded BLI sensor in exploratory measurements. Molecular docking and a single 100-ns molecular dynamics simulation suggested a possible suramin-binding mode near the electropositive groove. TcTV2 NP therefore combines a predicted phenuivirus-like core with experimentally observed RNA association and heterogeneous ring-like particle formation, while the computational analyses nominate the electropositive groove as a candidate surface for further ligand interaction studies.