I2BC External Speaker’s Seminar

Lundi 29 Juin à 11H00 

Salle N0-001 Bat 22

Stories of the non-structural proteins of influenza virus A

Alice Stelfox 

INRAE, Jouy-en-Josas

Abstract

The Influenza A virus (IAV) genome is composed of eight single-stranded, negative-sense RNA segments. The IAV NS segment encodes the multifunctional proteins NS1 and NEP, which play central roles in viral replication, host adaptation, and remodeling of the intracellular environment.

NEP regulates viral transcription and mediates nuclear export of viral ribonucleoprotein complexes (vRNPs) through the CRM1 pathway, a critical step in the IAV lifecycle that remains mechanistically unresolved. To structurally characterize NEP, artificial binding proteins (αReps) were generated against H1N1 NEP. Complex formation with αRepE4 enabled crystallization of full-length NEP and integrative structural analysis by X-ray crystallography and XL-MS. These data revealed a compact monomeric conformation, contrasting a previous elongated dimeric model. We further show that elevated temperature promotes assembly of the NEP–CRM1–RanGTP nuclear export complex, supporting a model in which NEP structural plasticity facilitates its multiple functions during infection.

In parallel, NS1 reshapes the host-cell environment through extensive interactions with cellular pathways involved in innate immunity and antiviral restriction. Certain avian IAV strains form ordered intracellular NS1 crystals near mitochondria as well diffuse accumulation in the nucleas, whereas mammalian-adapted strains instead only produce the less ordered nuclear assemblies. Our work suggests that these distinct NS1 ultrastructures correlate with differences in interferon antagonism, virulence, and host restriction, indicating that NS1 organization and sequestration may contribute to influenza pathogenesis and adaptation. Next, we are aim to describe in detail the crystal-mitochondria interactions using in situ structural biology techniques, potentially providing insight into mechanisms of host restriction and virulence.