Structure of importin-α bound to a non-classical nuclear localization signal of the influenza A virus nucleoprotein.

Ryohei Nakada,Yoshiyuki Matsuura,Hidemi Hirano

doi:10.1038/srep15055

Ryohei Nakada, Yoshiyuki Matsuura + Show 1 more

Open Access

https://doi.org/10.1038/srep15055

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Journal: Scientific reports	Publication Date: Oct 12, 2015
Citations: 44	License type: CC BY 4.0

Affiliation: Nagoya University

Abstract

A non-classical nuclear localization signal (ncNLS) of influenza A virus nucleoprotein (NP) is critical for nuclear import of viral genomic RNAs that transcribe and replicate in the nucleus of infected cells. Here we report a 2.3 Å resolution crystal structure of mouse importin-α1 in complex with NP ncNLS. The structure reveals that NP ncNLS binds specifically and exclusively to the minor NLS-binding site of importin-α. Structural and functional analyses identify key binding pockets on importin-α as potential targets for antiviral drug development. Unlike many other NLSs, NP ncNLS binds to the NLS-binding domain of importin-α weakly with micromolar affinity. These results suggest that a modest inhibitor with low affinity to importin-α could have anti-influenza activity with minimal cytotoxicity.

Highlights

A non-classical nuclear localization signal of influenza A virus nucleoprotein (NP) is critical for nuclear import of viral genomic RNAs that transcribe and replicate in the nucleus of infected cells
The NP non-classical nuclear localization signal (NLS) (ncNLS) is important for nuclear import of newly synthesized free NP proteins that are required for assembly of progeny vRNPs24–26
The NP ncNLS is exposed to solvent in the structural models of viral ribonucleoprotein (vRNP) based on electron microsopy (EM)[29,30], and it seems likely that multiple importin-α :β complexes are recruited to vRNP via binding to the ncNLS of NP

Summary

Introduction

A non-classical nuclear localization signal (ncNLS) of influenza A virus nucleoprotein (NP) is critical for nuclear import of viral genomic RNAs that transcribe and replicate in the nucleus of infected cells. Three lines of previously reported biochemical and cell biological data provided strong support for the proposal that the ncNLS is required for nuclear import of the NP protein via direct binding to importin-α , and that the ncNLS is functional in the context of the intact, full-length NP. Substitution of the basic residues of ncNLS (i.e., K7 and R8) with alanine abolished nuclear import of full-length NP25,26, and drastically weakened the binding of importin-α to full-length NP in GST pull-down assay[26].

Results

Conclusion