Dynamic structures of dengue virus serotype 2 secreted NS1 and their interactions with heparan sulfate.

Dengue secreted non-structural protein 1 (sNS1) contributes to the vascular permeability symptom of severe dengue hemorrhagic fever. Previous flavivirus sNS1 structures suggest that they predominantly exist as loose tetramers. Here, we report two stable tetramer structures (3.1-3.6 Å) together with loose tetramers. Formation of the stable tetramers involves a dramatic rearrangement of their N-terminal regions compared to the loose tetramers. We observe a higher molecular weight complex (HMWC) comprising dimeric sNS1 and heat shock proteins, which exhibits much lower endothelial hyperpermeability activity than the tetramer-enriched samples. We also determine high-resolution structures of the sNS1 complex with heparin, an analogue of the attachment factor heparan sulfate, showing that heparin binds to a conserved basic groove on the outer surface of the dimer, at the intra-dimer interface. Pre-incubation of sNS1 with heparin reduces its endothelial hyperpermeability activity. Our findings provide important structural information for future sNS1-based drug or vaccine design.