5wun
Crystal structure of mouse importin-alpha1 bound to non-phosphorylated NLS of EBNA1
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 PubMedEpstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is expressed in every EBV-positive tumor and is essential for the maintenance, replication, and transcription of the EBV genome in the nucleus of host cells. EBNA1 is a serine phosphoprotein, and it has been shown that phosphorylation of S385 in the nuclear localization signal (NLS) of EBNA1 increases the binding affinity to the nuclear import adaptor importin-alpha1 as well as importin-alpha5, and stimulates nuclear import of EBNA1. To gain insights into how phosphorylation of the EBNA1 NLS regulates nuclear import, we have determined the crystal structures of two peptide complexes of importin-alpha1: one with S385-phosphorylated EBNA1 NLS peptide, determined at 2.0 A resolution, and one with non-phosphorylated EBNA1 NLS peptide, determined at 2.2 A resolution. The structures show that EBNA1 NLS binds to the major and minor NLS-binding sites of importin-alpha1, and indicate that the binding affinity of the EBNA1 NLS to the minor NLS-binding site could be enhanced by phosphorylation of S385 through electrostatic interaction between the phosphate group of phospho-S385 and K392 of importin-alpha1 (corresponding to R395 of importin-alpha5) on armadillo repeat 8. Structural basis for the regulation of nuclear import of Epstein-Barr virus nuclear antigen 1 (EBNA1) by phosphorylation of the nuclear localization signal.,Nakada R, Hirano H, Matsuura Y Biochem Biophys Res Commun. 2017 Feb 26;484(1):113-117. doi:, 10.1016/j.bbrc.2017.01.063. Epub 2017 Jan 17. PMID:28104399[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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