The coiled-coil domain structure of the Sin Nombre virus nucleocapsid protein

Abstract

Hantaviruses can cause hemorrhagic fever with a renal syndrome and hantavirus pulmonary syndrome when transmitted to humans. The nucleocapsid protein of hantaviruses encapsidates viral genomic RNA and associates with transcription and replication complexes. Both the amino and carboxy termini of the nucleocapsid protein had been predicted to form trimers prior to the formation of the ribonucleoprotein. Crystal structures of amino-terminal fragments of the nucleocapsid protein showed the formation of intramolecular antiparallel coiled coils, but not intermolecular trimers. Thus, the amino-terminal part of the nucleocapsid protein is probably insufficient to initiate the trimerization of the full-length molecule.

Figure 1

The Bunyaviridae family. (a) Schematic drawing of a viral particle. The N protein binds all three segments of viral RNA and forms S, M, and L RNPs. (b) Cryo-EM micrograph of vitrified Hantaan virus particles [courtesy of Paul R. Chipman and Dr. Colleen B. Jonsson, unpublished results].

Figure 2

Fusion construct used for expression of truncated mutant 1–75 of the N protein.

Figure 3

Stereo pair showing chain B in the crystallographic asymmetric unit of the 1–75 fragment. The α-helix backbones are shown by a green tube. A black line represents the axis of the coiled coil. Ionic bridges between two α-helices are shown as yellow dashed lines. Several residues are labeled for clarity.

Figure 4

Coiled-coil heptad repeat alignment of the 1–75 fragment amino acid sequence. Positions a and d are predominantly occupied by hydrophobic residues. Charges are shown for residues in e positions, which form interhelical ionic bridges. Numbering is as in the N protein. Residues −2 to 0 are the amino acids that remain after cleavage of the helper molecule.

Figure 5

Two possible conformations of the 1–75 fragment as a part of the fusion molecule. (1) All three chains form a trimeric coiled coil with an insertion loop around residues 35-DPD-37. (2) Each chain independently forms an antiparallel coiled coil.