Molecular Basis of the Ternary Interaction between NS1 of the 1918 Influenza A Virus, PI3K, and CRK.

Alyssa Dubrow,Jae-Hyun Cho,Nowlan Savage,Qingliang Shen,Sirong Lin

doi:10.3390/v12030338

Abstract

The 1918 influenza A virus (IAV) caused the worst flu pandemic in human history. Non-structural protein 1 (NS1) is an important virulence factor of the 1918 IAV and antagonizes host antiviral immune responses. NS1 increases virulence by activating phosphoinositide 3-kinase (PI3K) via binding to the p85β subunit of PI3K. Intriguingly, unlike the NS1 of other human IAV strains, 1918 NS1 hijacks another host protein, CRK, to form a ternary complex with p85β, resulting in hyperactivation of PI3K. However, the molecular basis of the ternary interaction between 1918 NS1, CRK, and PI3K remains elusive. Here, we report the structural and thermodynamic bases of the ternary interaction. We find that the C-terminal tail (CTT) of 1918 NS1 remains highly flexible in the complex with p85β. Thus, the CTT of 1918 NS1 in the complex with PI3K can efficiently hijack CRK. Notably, our study indicates that 1918 NS1 enhances its affinity to p85β in the presence of CRK, which might result in enhanced activation of PI3K. Our results provide structural insight into how 1918 NS1 hijacks two host proteins simultaneously.

Highlights

The 1918 influenza A virus (1918 IAV) was responsible for the 1918 flu pandemic, which resulted in more than 50 million deaths worldwide [1]
non-structural protein 1 (NS1) consists of three structural units; the N-terminal RNA binding domain (RBD), an effector domain (ED), and a C-terminal tail (CTT) (Figure 1)
The RBD and ED are tethered by a flexible linker, and the CTT is structurally disordered; it was proposed that the conformational plasticity of NS1 is functionally important [9,10]

Summary

Introduction

The 1918 influenza A virus (1918 IAV) was responsible for the 1918 flu pandemic, which resulted in more than 50 million deaths worldwide [1]. All three structural units are heavily involved in the interaction with a number of host proteins [9], which is the basis of the multifunctional activity of NS1. Recent studies have suggested that the function of NS1 varies according to influenza strains [21–. I CARD domain while the interaction was not observed for the protein from the Udorn strain [25]. Domain while the interaction was not observed for the protein from the Udorn strain [25]. It was demonstrated that 1918 NS1 forms a ternary interaction with PI3K and CRK, resulting. It was demonstrated that 1918 NS1 forms a ternary interaction with PI3K and CRK, resulting in in enhanced activation of PI3K [22,29]. Our study reveals that the p85 hijacks CRK through a fuzzy electrostatic interaction mediated by its CTT.

Materials and Methods

Results and Discussion

Molecular