title: Distinctive conformation of minor site-specific nuclear localization signals bound to importin-α.
abstract: Nuclear localization signals (NLSs) contain one or two clusters of basic residues and are recognized by the import receptor importin-α. There are two NLS-binding sites (major and minor) on importin-α and the major NLS-binding site is considered to be the primary binding site. Here, we used crystallographic and biochemical methods to investigate the binding between importin-α and predicted 'minor site-specific' NLSs: four peptide library-derived peptides, and the NLS from mouse RNA helicase II/Guα. The crystal structures reveal that these atypical NLSs indeed preferentially bind to the minor NLS-binding site. Unlike previously characterized NLSs, the C-terminal residues of these NLSs form an α-helical turn, stabilized by internal H-bond and cation-π interactions between the aromatic residues from the NLSs and the positively charged residues from importin-α. This helical turn sterically hinders binding at the major NLS-binding site, explaining the minor-site preference. Our data suggest the sequence RXXKR[K/X][F/Y/W]XXAF as the optimal minor NLS-binding site-specific motif, which may help identify novel proteins with atypical NLSs.
authors.affiliation: School of Chemistry and Molecular Biosciences and Institute for Molecular Bioscience, University of Queensland, Brisbane, Qld, 4072, Australia; Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, Qld, 4072, Australia.
authors.forename: Chiung-Wen
authors.initials: CW
authors.lastname: Chang
authors.forename: Rafael Miguez
authors.initials: RM
authors.lastname: Couñago
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Williams
authors.forename: Mikael
authors.initials: M
authors.lastname: Bodén
authors.forename: Bostjan
authors.initials: B
authors.lastname: Kobe
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D051379:Mice; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020365:RNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D028901:alpha Karyopherins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D019913:Nuclear Localization Signals; D028901:alpha Karyopherins; D020365:RNA Helicases
keywords: RNA helicase II/Guα; crystal structure; importin-alpha; nuclear localization signal; nucleocytoplasmic transport