title: Identification of a karyopherin β1/β2 proline-tyrosine nuclear localization signal in huntingtin protein.
abstract: Among the known pathways of protein nuclear import, the karyopherin β2/transportin pathway is only the second to have a defined nuclear localization signal (NLS) consensus. Huntingtin, a 350-kDa protein, has defined roles in the nucleus, as well as a CRM1/exportin-dependent nuclear export signal; however, the NLS and exact pathway of import have remained elusive. Here, using a live cell assay and affinity chromatography, we show that huntingtin has a karyopherin β2-dependent proline-tyrosine (PY)-NLS in the amino terminus of the protein. This NLS comprises three consensus components: a basic charged sequence, a downstream conserved arginine, and a PY sequence. Unlike the classic PY-NLS, which has an unstructured intervening sequence between the consensus components, we show that a β sheet structured region separating the consensus elements is critical for huntingtin NLS function. The huntingtin PY-NLS is also capable of import through the importin/karyopherin β1 pathway but was not functional in all cell types tested. We propose that this huntingtin PY-NLS may comprise a new class of multiple import factor-dependent NLSs with an internal structural component that may regulate NLS activity.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada L8N3Z5.
authors.forename: Carly R
authors.initials: CR
authors.lastname: Desmond
authors.forename: Randy Singh
authors.initials: RS
authors.lastname: Atwal
authors.forename: Jianrun
authors.initials: J
authors.lastname: Xia
authors.forename: Ray
authors.initials: R
authors.lastname: Truant
mesh_terms: D000818:Animals; D006801:Humans; D000071058:Huntingtin Protein; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D019913:Nuclear Localization Signals / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010449:Peptide Mapping / Q000379:methods; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D028961:beta Karyopherins / Q000235:genetics* / Q000378:metabolism
chemical_list: C086055:HTT protein, human; C506812:Htt protein, mouse; D000071058:Huntingtin Protein; C424166:KPNB1 protein, human; C094999:Kpnb1 protein, mouse; D009419:Nerve Tissue Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C108121:TNPO1 protein, human; D028961:beta Karyopherins