Fig. 3. CryoEM structures of the recombinant sNS1 loose tetramer and hexamer.

a (i) The fit of sNS1 into the 8 Å resolution loose tetramer density map. (ii) Focused refinement of one dimer of the loose tetramer yields a 3.4 Å resolution map. An iNS1 dimer fits well into the density showing that the loose tetramer contains a β-roll structure similar to that of iNS1. Left: cryoEM map with the density corresponding to the β-roll colored in green and the rest in yellow. Right: the fit of the red/green dimer into the density. (iii) Superposition of our loose tetramer with the tetramer observed in the crystal packing of ZIKV sNS1 structure (PDB: 5GS6) shows that they have similar structures. b Comparison of our sNS1 hexamer with the dengue iNS1 hexamer from the crystal packing. (i) Top and side views of the 8 Å resolution sNS1 hexamer structure. Left: fit of three dimers into the cryoEM map. We are unable to discern whether sNS1 adopts a β-roll or an elongated β-sheet structure, as the interior of the hexamer contains unfeatured density. (ii) The previously published dengue iNS1 structure¹¹ shows hexamers due to crystal packing; however, there is little interaction between the iNS1 dimers (left; top view). The dimers in the hexamer (right; side view) are also oriented differently to our hexameric structure (in (i), side view). For the side view, the protomers within one dimer are colored in pink and green ribbons, and the other dimers are shown as white surface representations. c Interaction of a loose tetramer with a dimer could lead to the formation of a hexamer.