Structure- Function Studies Of Flavivirus Non-Structural Protein1

Abstract

Flaviviruses is a genus within the family Flaviviridae. The genus consists of more than 70 viruses, including important threatening human pathogens such as dengue virus (DENV), West Nile virus (WNV), and Zika virus (ZIKV). These viruses are causative agents for a range of mild to lethal diseases and there are currently no US- licensed therapeutic treatments for infection. The virus genome is a positive-sense, single-stranded RNA, encoding ten viral proteins. Of the ten flavivirus proteins, Non- Structural protein 1 (NS1) remains the most elusive in terms of its functions. To date NS1 has been linked to disease pathology and progression and plays roles in virus replication and assembly. However, little is understood how NS1 orchestrates these functions and how NS1 from different viruses function distinctively from one another. Moreover, flavivirus NS1 has a peculiar ability to associate with lipid membranes. During the life cycle of NS1, the protein travels through the classical secretory path- way, similar to infectious virus particles, and is secreted into the extracellular space as mostly hexameric oligomers containing a lipid core. How the protein binds to lipids and whether such lipid binding is important for NS1 functions and overall flavivirus pathology remain unknown. Using structure-based mutagenesis, we found a group of mutants on WNV NS1, which particularly altered the viral specific infectivity but maintained wild-type level of virus replication. Purified mutated virus particles revealed that the specific infectivity alteration was not because of the particle but interaction of the virus particles and NS1 mutated proteins. Here we demonstrated that specific residues on NS1 were responsible for distinctly roles in NS1 functions and the virus specific infectivity was regulated by NS1 protein. In other structure-base study, we focused on the membrane association ability of NS1. All structure-predicted regions on NS1 were examined for its contribution for the membrane/lipid binding function. This interaction was required for NS1 biology activities including intracel- lular trafficking, oligomerization, and endocytosis. The lipidomes from deletion of each membrane association region revealed differences in lipid classes binding to each region and the composition flexiblity of the lipid cargo of NS1 hexamer.