title: A short N-terminal peptide motif on flavivirus nonstructural protein NS1 modulates cellular targeting and immune recognition.
abstract: Flavivirus NS1 is a versatile nonstructural glycoprotein, with intracellular NS1 functioning as an essential cofactor for viral replication and cell surface and secreted NS1 antagonizing complement activation. Even though NS1 has multiple functions that contribute to virulence, the genetic determinants that regulate the spatial distribution of NS1 in cells among different flaviviruses remain uncharacterized. Here, by creating a panel of West Nile virus-dengue virus (WNV-DENV) NS1 chimeras and site-specific mutants, we identified a novel, short peptide motif immediately C-terminal to the signal sequence cleavage position that regulates its transit time through the endoplasmic reticulum and differentially directs NS1 for secretion or plasma membrane expression. Exchange of two amino acids within this motif reciprocally changed the cellular targeting pattern of DENV or WNV NS1. For WNV, this substitution also modulated infectivity and antibody-induced phagocytosis of infected cells. Analysis of a mutant lacking all three conserved N-linked glycosylation sites revealed an independent requirement of N-linked glycans for secretion but not for plasma membrane expression of WNV NS1. Collectively, our experiments define the requirements for cellular targeting of NS1, with implications for the protective host responses, immune antagonism, and association with the host cell sorting machinery. These studies also suggest a link between the effects of NS1 on viral replication and the levels of secreted or cell surface NS1.
authors.affiliation: Department of Medicine, Washington University School of Medicine, 660 South Euclid Ave., Saint Louis, MO 63110, USA.
authors.forename: Soonjeon
authors.initials: S
authors.lastname: Youn
authors.forename: Hyelim
authors.initials: H
authors.lastname: Cho
authors.forename: Daved H
authors.initials: DH
authors.lastname: Fremont
authors.forename: Michael S
authors.initials: MS
authors.lastname: Diamond
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D009033:Culicidae; D003716:Dengue Virus / Q000235:genetics; D005416:Flavivirus / Q000276:immunology* / Q000472:pathogenicity*; D057131:Immune Evasion; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000502:physiology*; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*; D014902:West Nile virus / Q000235:genetics
chemical_list: D050505:Mutant Proteins; C100315:NS1 protein, Flavivirus; D011994:Recombinant Proteins; D017361:Viral Nonstructural Proteins; D037521:Virulence Factors