PMID: 21388519 , Related PDB id: 3OQS

Authors:

Mynott AV, Harrop SJ, Brown LJ, Breit SN, Kobe B, Curmi PM

Title:

Crystal structure of importin-alpha bound to a peptide bearing the nuclear localisation signal from chloride intracellular channel protein 4.

Journal:

FEBS J. 2011 May;278(10):1662-75. doi: 10.1111/j.1742-4658.2011.08086.x., Epub 2011 Mar 30.

Abstract:

It has been reported that a human chloride intracellular channel (CLIC) protein, CLIC4, translocates to the nucleus in response to cellular stress, facilitated by a putative CLIC4 nuclear localization signal (NLS). The CLIC4 NLS adopts an alpha-helical structure in the native CLIC4 fold. It is proposed that CLIC4 is transported to the nucleus via the classical nuclear import pathway after binding the import receptor, importin-alpha. In this study, we have determined the X-ray crystal structure of a truncated form of importin-alpha lacking the importin-beta binding domain, bound to a CLIC4 NLS peptide. The NLS peptide binds to the major binding site in an extended conformation similar to that observed for the classical simian virus 40 large T-antigen NLS. A Tyr residue within the CLIC4 NLS makes surprisingly favourable interactions by forming side-chain hydrogen bonds to the importin-alpha backbone. This structural evidence supports the hypothesis that CLIC4 translocation to the nucleus is governed by the importin-alpha nuclear import pathway, provided that CLIC4 can undergo a conformational rearrangement that exposes the NLS in an extended conformation.