title: Nonstructural Proteins Are Preferential Positive Selection Targets in Zika Virus and Related Flaviviruses.
abstract: The Flavivirus genus comprises several human pathogens such as dengue virus (DENV), Japanese encephalitis virus (JEV), and Zika virus (ZIKV). Although ZIKV usually causes mild symptoms, growing evidence is linking it to congenital birth defects and to increased risk of Guillain-Barré syndrome. ZIKV encodes a polyprotein that is processed to produce three structural and seven nonstructural (NS) proteins. We investigated the evolution of the viral polyprotein in ZIKV and in related flaviviruses (DENV, Spondweni virus, and Kedougou virus). After accounting for saturation issues, alignment uncertainties, and recombination, we found evidence of episodic positive selection on the branch that separates DENV from the other flaviviruses. NS1 emerged as the major selection target, and selected sites were located in immune epitopes or in functionally important protein regions. Three of these sites are located in an NS1 region that interacts with structural proteins and is essential for virion biogenesis. Analysis of the more recent evolutionary history of ZIKV lineages indicated that positive selection acted on NS5 and NS4B, this latter representing the preferential target. All selected sites were located in the N-terminal portion of NS4B, which inhibits interferon response. One of the positively selected sites (26M/I/T/V) in ZIKV also represents a selection target in sylvatic DENV2 isolates, and a nearby residue evolves adaptively in JEV. Two additional positively selected sites are within a protein region that interacts with host (e.g. STING) and viral (i.e. NS1, NS4A) proteins. Notably, mutations in the NS4B region of other flaviviruses modulate neurovirulence and/or neuroinvasiveness. These results suggest that the positively selected sites we identified modulate viral replication and contribute to immune evasion. These sites should be prioritized in future experimental studies. However, analyses herein detected no selective events associated to the spread of the Asian/American ZIKV lineage.
authors: Scientific Institute IRCCS E. MEDEA, Bioinformatics, Bosisio Parini, Italy.
authors: Manuela
authors: M
authors: Sironi
authors: Scientific Institute IRCCS E. MEDEA, Bioinformatics, Bosisio Parini, Italy.
authors: Diego
authors: D
authors: Forni
authors: Department of Physiopathology and Transplantation, University of Milan, Milan, Italy.|Don C. Gnocchi Foundation ONLUS, IRCCS, Milan, Italy.
authors: Mario
authors: M
authors: Clerici
authors: Scientific Institute IRCCS E. MEDEA, Bioinformatics, Bosisio Parini, Italy.
authors: Rachele
authors: R
authors: Cagliani
mesh_terms: D000939:Epitopes / Q000235:genetics*; D006801:Humans; D057131:Immune Evasion; D010802:Phylogeny; D017361:Viral Nonstructural Proteins / Q000235:genetics*; D014779:Virus Replication; D000071244:Zika Virus / Q000235:genetics* / Q000502:physiology*; D000071243:Zika Virus Infection / Q000821:virology
chemical_list: D000939:Epitopes; C100315:NS1 protein, Flavivirus; C080107:NS4B protein, flavivirus; C096041:NS5 protein, flavivirus; D017361:Viral Nonstructural Proteins