5ctt
Crystal structure of human SART3/TIP110 NLS-mouse importin alpha complex
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 PubMedSquamous cell carcinoma antigen recognized by T-cells 3 (SART3) is a U4/U6 recycling factor as well as a targeting factor of USP4 and USP15. However, the details of how SART3 recognizes these deubiquitinases and how they get subsequently translocated into the nucleus are not known. Here, we present the crystal structures of the SART3 half-a-tetratricopeptide (HAT) repeat domain alone and in complex with the domain present in ubiquitin-specific protease (DUSP)-ubiquitin-like (UBL) domains of ubiquitin specific protease 4 (USP4). The 12 HAT repeats of SART3 are in two sub-domains (HAT-N and HAT-C) forming a dimer through HAT-C. USP4 binds SART3 at the opposite surface of the HAT-C dimer interface utilizing the beta-structured linker between the DUSP and the UBL domains. The binding affinities of USP4 and USP15 to SART3 are 0.9 muM and 0.2 muM, respectively. The complex structure of SART3 nuclear localization signal (NLS) and importin-alpha reveals bipartite binding, and removal of SART3 NLS prevents the entry of USP4 (and USP15) into the nucleus and abrogates the subsequent deubiquitinase activity of USP4. Structural basis for recruiting and shuttling of the spliceosomal deubiquitinase USP4 by SART3.,Park JK, Das T, Song EJ, Kim EE Nucleic Acids Res. 2016 Apr 7. pii: gkw218. PMID:27060135[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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