6wbc
Structure of Mouse Importin alpha- MLH1-R472K NLS Peptide 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 PubMedThe classical nuclear import pathway is mediated by importin (Impalpha and Impbeta), which recognizes the cargo protein by its nuclear localization sequence (NLS). NLSs have been extensively studied resulting in different proposed consensus; however, recent studies showed that exceptions may occur. This mechanism may be also dependent on specific characteristics of different Impalpha. Aiming to better understand the importance of specific residues from consensus and adjacent regions of NLSs, we studied different mutations of a high-affinity NLS complexed to Impalpha by crystallography and calorimetry. We showed that although the consensus sequence allows Lys or Arg residues at the second residue of a monopartite sequence, the presence of Arg is very important to its binding in major and minor sites of Impalpha. Mutations in the N or C-terminus (position P1 or P6) of the NLS drastically reduces their affinity to the receptor, which is corroborated by the loss of hydrogen bonds and hydrophobic interactions. Surprisingly, a mutation in the far N-terminus of the NLS led to an increase in the affinity for both binding sites, corroborated by the structure with an additional hydrogen bond. The binding of NLSs to the human variant Impalpha1 revealed that these are similar to those found in structures presented here. For human variant Impalpha3, the bindings are only relevant for the major site. This study increases understanding of specific issues sparsely addressed in previous studies that are important to the task of predicting NLSs, which will be relevant in the eventual design of synthetic NLSs. Structural and calorimetric studies reveal specific determinants for the binding of a high-affinity NLS to mammalian importin-alpha.,de Oliveira HC, da Silva TD, Salvador GHM, Moraes IR, Fukuda CA, de Barros AC, Fontes MRM Biochem J. 2021 Jul 16;478(13):2715-2732. doi: 10.1042/BCJ20210401. PMID:34195786[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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