Distinctive Conformation of Minor Site-Specific Nuclear Localization Signals Bound to Importin-α

Chiung Wen Chang, Rafael Miguez Couñago, Simon J. Williams, Mikael Bodén, Bostjan Kobe*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)

Abstract

Nuclear localization signals (NLSs) contain one or two clusters of basic residues that are recognized by importin-α. Importin-α has two NLS-binding sites (major and minor), with the major site known as the primary binding site. Using crystallographic and biochemical approaches, we have characterized a group of atypical NLSs that bind primarily to the minor site. Unlike previously characterized NLSs, the C-terminal residues of these NLSs form an α-helical turn, which prevents them from binding to the major NLS-binding site. 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.

Original languageEnglish
Pages (from-to)1144-1154
Number of pages11
JournalTraffic
Volume14
Issue number11
DOIs
Publication statusPublished - Nov 2013
Externally publishedYes

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