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Crystal structure of importin-alpha1 bound to the 53BP1 nuclear localization signal (wild-type)
Structural highlights
FunctionIMA1_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 PubMed53BP1 (TP53-binding protein 1) plays a key role in DNA double-strand break repair by promoting non-homologous end joining (NHEJ) especially during G1 phase of the cell cycle. Nuclear import of 53BP1 is required for proper localization of 53BP1 and maintenance of genome integrity. 53BP1 has a classical bipartite nuclear localization signal (NLS) of sequence 1666-GKRKLITSEEERSPAKRGRKS-1686. Ser1678 within the 53BP1 NLS can be phosphorylated by CDK1/cyclin B, and a phosphomimetic substitution of Ser1678 with aspartate has been shown to negatively regulate nuclear import of 53BP1. Here, the X-ray crystal structures of the nuclear import adaptor importin-alpha1 bound to the wild-type 53BP1 NLS and the S1678D mutant of 53BP1 NLS are reported at resolutions of 1.9 and 1.7A, respectively. In the wild-type structure, not only the two basic clusters of the 53BP1 NLS but also the linker region between the basic clusters made extensive interactions with importin-alpha1. In the mutant structure, the linker region between the basic clusters in the 53BP1 NLS made fewer interactions with importin-alpha1 than those observed in the wild-type structure. However, biochemical binding assays using purified proteins showed that the 53BP1 mutation S1678D reduces the binding affinity to importin-alpha1 only to a modest extent. Implications of these findings for regulatory mechanism of 53BP1 nuclear import are discussed. Structural and biochemical characterization of the recognition of the 53BP1 nuclear localization signal by importin-alpha.,Matsuura Y Biochem Biophys Res Commun. 2019 Mar 5;510(2):236-241. doi:, 10.1016/j.bbrc.2019.01.075. Epub 2019 Jan 23. PMID:30685087[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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