Fig. 3: Structure of SFTSV Gn/Gc heterodimer.

a Schematic diagram of the domain architecture of Gn and Gc in the context of the glycoprotein precursor. Each domain is represented by a unique color, and the glycosylation sites are indicated by small branches. The signal peptide (SP) of Gn and the internal signal peptide (ISP) of Gc are colored in dark gray, and the linker between Gn and Gc is outlined with red dashed lines. b, c The cryo-EM density map b and atomic model c of SFTSV Gn/Gc heterodimer colored by domains, with the same code as in a. The N-linked glycans are colored in black, and the fusion loops are highlighted in green. The blue and black dashed boxes indicate the key interaction interfaces between Gn and Gc, for which the details are shown in e–g. d Density map of the glycans in close-up views. The red asterisk indicates the unmodeled density for additional glycan residues. e–g Molecular interactions at the Gn/Gc interface. The structures are shown in cartoons and colored by domains as in a. The residues potentially involved in Gn/Gc interactions are shown as sticks and colored by elements. In e, the dashed lines represent the hydrogen bonds between Gc b-strand and the adjacent Gn strand in the β-connector domain. The distances between hydrogen donor and acceptor atoms are labeled with red numbers (in Å). In f, the electrostatic potential surface of Gn is shown to depict the complementary charge pattern with Gc residues. In g, the Gn domain C and Gc domain I and domain II are shown in surface, and the long Gc linker is presented with ribbon model which inserts into the crevice between Gn domain C and Gc domain II. h Structure of the fusion loops in SFTSV Gc. The structure is colored by domains and the fusion loop regions are colored in green. The key hydrophobic residues (green) and cysteines (magenta) are shown as sticks. i Superposition of Gc structures before (colored by domains) and after (white) membrane fusion in the fusion loop region. The conformational changes of the fusion loops and key residues are indicated by arrows. j Comparison of SFTSV Gc structures in the pre- (left) and post-fusion (right) conformations. The hinge region between domain II and domain I is highlighted with an arrow, which becomes extended in the postfusion conformation. The directions for domain movement are indicated by curved arrows.