Oligomerization of hantavirus nucleocapsid protein: analysis of the N-terminal coiled-coil domain

Hantaviruses constitute a genus in the family Bunyaviridae. They are enveloped negative-strand RNA viruses with a tripartite genome encoding the nucleocapsid (N) protein, the two surface glycoproteins Gn and Gc, and an RNA-dependent RNA polymerase. The N protein is the most abundant component of the virion; it encapsidates genomic RNA segments forming ribonucleoproteins and participates in genome transcription and replication as well as virus assembly. In the course of RNA encapsidation, N protein forms intermediate trimers via head-to-head and tail-to-tail interactions. We analyzed the amino-terminal trimerization domain (amino acid residues 1 to 77) of Tula hantavirus using computer modeling, mammalian two-hybrid assay, and immunofluorescence assay. The results obtained were consistent with the existence of an antiparallel coiled-coil stabilized by interactions between hydrophobic residues. Residues L44, V51, and L58 were important for the N-N interaction; other residues, e.g., L25 and V32, also made a contribution, albeit a modest one. Our alignments of the N-terminal domain of the hantaviral N proteins suggest the coiled-coil structure, and hence the mode of N-protein oligomerization, is conserved among hantaviruses.