1y2a
From Proteopedia
Structure of mammalian importin bound to the non-classical PLSCR1-NLS
Structural highlights
Function[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. [PLS1_HUMAN] May mediate accelerated ATP-independent bidirectional transbilayer migration of phospholipids upon binding calcium ions that results in a loss of phospholipid asymmetry in the plasma membrane. May play a central role in the initiation of fibrin clot formation, in the activation of mast cells and in the recognition of apoptotic and injured cells by the reticuloendothelial system.[1] [2] May play a role in the antiviral response of interferon (IFN) by amplifying and enhancing the IFN response through increased expression of select subset of potent antiviral genes. May contribute to cytokine-regulated cell proliferation and differentiation.[3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedNuclear import of proteins containing a classical nuclear localization signal (NLS) is an energy-dependent process that requires the heterodimer importin alpha/beta. Three to six basic contiguous arginine/lysine residues characterize a classical NLS and are thought to form a basic patch on the surface of the import cargo. In this study, we have characterized the NLS of phospholipid scramblase 1 (PLSCR1), a lipid-binding protein that enters the nucleus via the nonclassical NLS (257)GKISKHWTGI(266). This import sequence lacks a contiguous stretch of positively charged residues, and it is enriched in hydrophobic residues. We have determined the 2.2 A crystal structure of a complex between the PLSCR1 NLS and the armadillo repeat core of vertebrate importin alpha. Our crystallographic analysis reveals that PLSCR1 NLS binds to armadillo repeats 1-4 of importin alpha, but its interaction partially overlaps the classical NLS binding site. Two PLSCR1 lysines occupy the canonical positions indicated as P2 and P5. Moreover, we present in vivo evidence that the critical lysine at position P2, which is essential in other known NLS sequences, is dispensable in PLSCR1 NLS. Taken together, these data provide insight into a novel nuclear localization signal that presents a distinct motif for binding to importin alpha. Phospholipid scramblase 1 contains a nonclassical nuclear localization signal with unique binding site in importin alpha.,Chen MH, Ben-Efraim I, Mitrousis G, Walker-Kopp N, Sims PJ, Cingolani G J Biol Chem. 2005 Mar 18;280(11):10599-606. Epub 2004 Dec 17. PMID:15611084[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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