Influenza A virus NS1 protein binds as a dimer to the RNA-free PABP1 but not to the PABP1-Poly(A) RNA Complex

Abstract

Influenza A virus (IAV) is a highly contagious human pathogen responsible for nearly half a million deaths each year. Non-structural protein 1 (NS1) is a crucial protein expressed by IAV to evade the host immune system. Additionally, NS1 has been proposed to stimulate translation because of its ability to bind poly(A) binding protein 1 (PABP1) and eukaryotic initiation factor 4G (eIF4G). We analyzed the interaction of NS1 with PABP1 using quantitative techniques. Our studies show that NS1 binds as a homodimer to PABP1, and this interaction is conserved across different IAV strains. Unexpectedly, NS1 does not bind to PABP1 that is bound to poly(A) RNA. Instead, NS1 only binds to PABP1 free of RNA, suggesting that translation stimulation does not occur by NS1 interacting with the PABP1 molecule attached to the mRNA 3-poly(A) tail. We propose that NS1 binds to the eIF4G complex at the 5-end of the mRNA and recruits the RNA-free PABP1, which may stimulate translation initiation by promoting the association of the ribosomal subunits.