title: Structural basis of Flavivirus NS1 assembly and antibody recognition.
abstract: The Flavivirus nonstructural protein 1 (NS1) is a conserved, membrane-associated and secreted glycoprotein with replication and immune evasion functions. Secreted NS1 is a hexameric, barrel-shaped lipoprotein that can bind back to the plasma membrane of cells. Antibodies targeting cell surface-associated NS1 can be protective in vivo in a manner dependent on Fc effector functions. We describe here the crystal structure of a C-terminal fragment (residues 172-352) of West Nile (WNV) and Dengue virus NS1 proteins at 1.85 and 2.7 Å resolution, respectively. NS1(172-352) assembles as a unique rod-shaped dimer composed of a 16-stranded β-platform flanked on one face by protruding connecting loops. We also determined the 3.0 Å resolution structure of WNV NS1(172-352) with the protective 22NS1 antibody Fab, which engages the loop-face of the rod. The head-to-head NS1(172-352) dimer we observe in crystal lattices is supported by multiangle light and small-angle X-ray scattering studies. We used the available cryo-electron microscopy reconstruction to develop a pseudoatomic model of the NS1 hexamer. The model was constructed with the NS1(172-352) dimeric rod aligned with the long axis of the barrel, and with the loop-face oriented away from the core. Difference densities suggest that the N-terminal region of NS1 forms globular lobes that mediate lateral contacts between dimers in the hexamer. Our model also suggests that the N-terminal lobe forms the surface of the central cavity where lipid binding may occur.
authors.affiliation: Departments of Pathology and Immunology, Medicine, Molecular Microbiology, and Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO 63110.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Edeling
authors.forename: Michael S
authors.initials: MS
authors.lastname: Diamond
authors.forename: Daved H
authors.initials: DH
authors.lastname: Fremont
mesh_terms: D000595:Amino Acid Sequence; D000914:Antibodies, Viral / Q000737:chemistry* / Q000276:immunology; D020285:Cryoelectron Microscopy; D003460:Crystallization; D003716:Dengue Virus / Q000235:genetics* / Q000276:immunology; D019281:Dimerization; D015967:Gene Expression Regulation, Viral / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D017361:Viral Nonstructural Proteins / Q000737:chemistry* / Q000276:immunology; D014902:West Nile virus / Q000235:genetics* / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D017361:Viral Nonstructural Proteins; C531936:nonstructural protein 1, West Nile virus
keywords: human pathogen; immune epitope; structural biology; virology