Flavivirus NS1 Structures Reveal Surfaces for Associations with Membranes and the Immune System

Abstract

Flaviviruses, the human pathogens responsible for dengue fever, West Nile fever, tick-borne encephalitis and yellow fever, are endemic in tropical and temperate parts of the world. The flavivirus non-structural protein 1 (NS1) functions in genome replication as an intracellular dimer and in immune system evasion as a secreted hexamer. We report crystal structures for full-length, glycosylated NS1 from West Nile and dengue viruses. The NS1 hexamer in crystal structures is similar to a solution hexamer visualized by single-particle electron microscopy. Recombinant NS1 binds to lipid bilayers and remodels large liposomes into lipoprotein nanoparticles. The NS1 structures reveal distinct domains for membrane association of the dimer and interactions with the immune system, and are a basis for elucidating the molecular mechanism of NS1 function.

The mechanism by which P250L mutation impairs flavivirus-NS1 dimerization: an investigation based on molecular dynamics simulations

“…Each monomer of the β-ladder domain is composed of 9 β strands on one face and residues that lack a well-defined secondary structure on the other face. The latter is commonly referred to as the "spaghetti loop" region (Akey et al 2014). Oligomerization of NS1 is observed in all flaviviruses and the dimeric form of this protein appears to play a role in flavivirus virulence.…”

“…Figure 2a shows the root-meansquare deviations (RMSD) calculated considering the backbone atoms of the WT and P250L monomers with respect to the crystal structure (Akey et al 2014). The WT simulation converged to a RMSD value of ∼0.11 nm after ∼0.3 ns and remained stable throughout the entire simulation, while the P250L simulation exhibited an accentuated increase of its RMSD value after ∼5 ns stabilizing at a deviation of ∼0.15 nm.…”

“…The side chain of the mutated residue, probably by means of a steric effect, pushed away the imidazole ring of H195 Fig. 3 a The interface region between the two NS1 β-ladder monomers as extracted from the DENV2 NS1 crystal structure (PDB code: 4O6B) (Akey et al 2014) is shown in a cartoon representation (hydrogen atoms were added to improve visualization). Residues A186 and I188 are shown in ball-and-stick representation and the four complementary hydrogen bonds between the two β1-strands are represented by dashed lines.…”

“…2 General structural features of WT and P250L β-ladder domains of NS1 on the course of the 100-ns molecular dynamics simulations. a The backbone root-mean-square deviations (RMSD) with respect to the crystal structure (Akey et al 2014). b The superposed final structures (WT in green, P250L in red) after least-squares fitting based on all backbone atoms.…”

“…1 Three-dimensional illustration of the NS1 dimer and its domains. The coordinates were extracted from the DENV2 NS1 crystal structure (Akey et al 2014) under PDB code 4O6B. a On the left side, a surface representation (in two different orientations) showing the extended β-ladder in green, the β-roll in blue, the wing in orange, and the connector region in violet.…”