3oqs
From Proteopedia
Crystal structure of importin-alpha bound to a CLIC4 NLS peptide
Structural highlights
Function[CLIC4_HUMAN] Can insert into membranes and form poorly selective ion channels that may also transport chloride ions. Channel activity depends on the pH. Membrane insertion seems to be redox-regulated and may occur only under oxydizing conditions. Promotes cell-surface expression of HRH3. Has alternate cellular functions like a potential role in angiogenesis or in maintaining apical-basolateral membrane polarity during mitosis and cytokinesis. Could also promote endothelial cell proliferation and regulate endothelial morphogenesis (tubulogenesis).[1] [2] [3] [4] [5] [6] [IMA2_MOUSE] Functions in nuclear protein import as an adapter protein for nuclear receptor KPNB1. Binds specifically and directly to substrates containing either a simple or bipartite NLS motif. Docking of the importin/substrate complex to the nuclear pore complex (NPC) is mediated by KPNB1 through binding to nucleoporin FxFG repeats and the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin-beta and the three components separate and importin-alpha and -beta are re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran from importin. The directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Publication Abstract from PubMedIt 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. Crystal structure of importin-alpha bound to a peptide bearing the nuclear localisation signal from chloride intracellular channel protein 4.,Mynott AV, Harrop SJ, Brown LJ, Breit SN, Kobe B, Curmi PM FEBS J. 2011 May;278(10):1662-75. doi: 10.1111/j.1742-4658.2011.08086.x., Epub 2011 Mar 30. PMID:21388519[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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