# Nonstructural Protein 1 of Influenza A (NS1A) Demonstrates Strain-Specific dsRNA Binding Capabilities

## TL;DR

This study shows that the NS1A protein from the 1918 Spanish Flu has unique RNA binding features that may explain its high pathogenicity.

## Contribution

The study reveals strain-specific dsRNA binding residues in the NS1A protein of the 1918 flu strain.

## Key findings

- A/Brevig Mission/1/1918 NS1A has RBD residues that enhance dsRNA binding.
- Both Brevig Mission and Udorn NS1A bind dsRNA via the C-terminal tail of the ED.
- These interactions may explain the 1918 flu's increased pathogenicity and impact antiviral design.

## Abstract

Nonstructural protein 1 of influenza A (NS1A) is a key
virulence
factor produced inside host cells infected with Influenza A Virus
(IAV) and consists of an N-terminal dsRNA binding domain (RBD) and
a C-terminal effector domain (ED), joined by a flexible linker. While
NS1A is a highly promiscuous protein with a number of intracellular
functions, its primary function is nonspecific dsRNA binding that
enables influenza to evade our innate immune system. For this reason,
NS1A has long been proposed as a potential drug target. Previous research
in the field has demonstrated the necessity of dimer formation through
the RBD to enable dsRNA binding, which is further enhanced by oligomerization
through ED interactions. However, there has been minimal exploration
of potential strain-specific effects on dsRNA binding. Most existing
studies are limited to the A/Udorn/307/1972 strain, often with a C-terminal
tail deletion. Here we utilize fluorescence polarization (FP) paired
with fluorescence-based electrophoretic mobility shift assays (fEMSA)
to characterize the dsRNA binding properties of NS1A from the H1N1
strain responsible for the 1918 “Spanish Flu” with an
intact C-terminal tail. We show that A/Brevig Mission/1/1918 NS1A
contains specific residues in the RBD that enhance dsRNA binding.
We further demonstrate that both Brevig Mission and Udorn NS1A bind
directly to dsRNA through the highly basic C-terminal tail of the
ED. These novel binding interactions may have contributed to the increased
pathogenicity of the 1918 flu pandemic and may have implications for
NS1A-targeted antivirals.