title: Polyglutamine domain flexibility mediates the proximity between flanking sequences in huntingtin.
abstract: Huntington disease (HD) is a neurodegenerative disorder caused by a CAG expansion within the huntingtin gene that encodes a polymorphic glutamine tract at the amino terminus of the huntingtin protein. HD is one of nine polyglutamine expansion diseases. The clinical threshold of polyglutamine expansion for HD is near 37 repeats, but the mechanism of this pathogenic length is poorly understood. Using Förster resonance energy transfer, we describe an intramolecular proximity between the N17 domain and the downstream polyproline region that flanks the polyglutamine tract of huntingtin. Our data support the hypothesis that the polyglutamine tract can act as a flexible domain, allowing the flanking domains to come into close spatial proximity. This flexibility is impaired with expanded polyglutamine tracts, and we can detect changes in huntingtin conformation at the pathogenic threshold for HD. Altering the structure of N17, either via phosphomimicry or with small molecules, also affects the proximity between the flanking domains. The structural capacity of N17 to fold back toward distal regions within huntingtin requires an interacting protein, protein kinase C and casein kinase 2 substrate in neurons 1 (PACSIN1). This protein has the ability to bind both N17 and the polyproline region, stabilizing the interaction between these two domains. We also developed an antibody-based FRET assay that can detect conformational changes within endogenous huntingtin in wild-type versus HD fibroblasts. Therefore, we hypothesize that wild-type length polyglutamine tracts within huntingtin can form a flexible domain that is essential for proper functional intramolecular proximity, conformations, and dynamics.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada L8N 3Z5.
authors.forename: Nicholas Stephane
authors.initials: NS
authors.lastname: Caron
authors.forename: Carly Robyn
authors.initials: CR
authors.lastname: Desmond
authors.forename: Jianrun
authors.initials: J
authors.lastname: Xia
authors.forename: Ray
authors.initials: R
authors.lastname: Truant
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D002478:Cells, Cultured; D005091:Exons / Q000235:genetics; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010455:Peptides / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; C492182:PACSIN1 protein, human; D010455:Peptides; C011083:polyproline; C097188:polyglutamine
keywords: FLIM-FRET; conformational switching; fluorescence lifetime imaging microscopy; neurodegeneration; polyglutamine diseases
references.citation: Nat Cell Biol. 2010 Jul;12(7):703-10
references.pmid: 20526328
references.citation: Proc Natl Acad Sci U S A. 2006 Jul 18;103(29):11045-50
references.pmid: 16832050
references.citation: Trends Pharmacol Sci. 2002 Jan;23(1):32-9
references.pmid: 11804649
references.citation: J Microsc. 2004 Jul;215(Pt 1):1-12
references.pmid: 15230870
references.citation: Gene. 1999 Oct 1;238(2):291-300
references.pmid: 10570957
references.citation: Eur J Biochem. 1998 Aug 15;256(1):201-11
references.pmid: 9746365
references.citation: FEBS J. 2007 Feb;274(3):773-82
references.pmid: 17288557
references.citation: Neuron. 2009 Dec 24;64(6):828-40
references.pmid: 20064390
references.citation: Nature. 1995 Nov 23;378(6555):403-6
references.pmid: 7477379
references.citation: FEBS J. 2008 Sep;275(17):4252-62
references.pmid: 18637947
references.citation: Anal Biochem. 2009 Dec 1;395(1):8-15
references.pmid: 19664996
references.citation: Nat Chem Biol. 2011 May 29;7(7):453-60
references.pmid: 21623356
references.citation: Proc Natl Acad Sci U S A. 2012 Feb 28;109(9):3528-33
references.pmid: 22331905
references.citation: J Cell Biol. 2009 Dec 28;187(7):1083-99
references.pmid: 20026656
references.citation: Nat Struct Mol Biol. 2007 Apr;14(4):332-40
references.pmid: 17369839
references.citation: Hum Mol Genet. 2007 Jan 1;16(1):61-77
references.pmid: 17135277
references.citation: J Biol Chem. 2013 Mar 29;288(13):9303-12
references.pmid: 23420842
references.citation: Adv Exp Med Biol. 2012;725:1-14
references.pmid: 22399315
references.citation: Hum Mol Genet. 2011 May 15;20(10):1937-51
references.pmid: 21355047
references.citation: Nat Genet. 1993 Aug;4(4):393-7
references.pmid: 8401588
references.citation: Hum Mol Genet. 2002 Oct 1;11(21):2547-58
references.pmid: 12354780
references.citation: Hum Mol Genet. 1993 Oct;2(10):1547-9
references.pmid: 8268907
references.citation: J Biol Chem. 2006 Nov 24;281(47):35608-15
references.pmid: 16973603
references.citation: PLoS One. 2012;7(8):e44159
references.pmid: 22952912
references.citation: PLoS One. 2010 Feb 04;5(2):e9053
references.pmid: 20140226
references.citation: Neurobiol Dis. 2008 Jun;30(3):365-374
references.pmid: 18417352
references.citation: Structure. 2009 Sep 9;17(9):1205-12
references.pmid: 19748341
references.citation: Nat Genet. 1993 Aug;4(4):387-92
references.pmid: 8401587
references.citation: Nat Neurosci. 2006 May;9(5):611-21
references.pmid: 16617342
references.citation: Biochemistry. 2006 Nov 7;45(44):13183-92
references.pmid: 17073440
references.citation: Hum Mol Genet. 2007 Nov 1;16(21):2600-15
references.pmid: 17704510
references.citation: Microsc Microanal. 2006 Jun;12(3):238-54
references.pmid: 17481360
references.citation: Cell. 1993 Mar 26;72(6):971-83
references.pmid: 8458085
references.citation: Cell Signal. 2004 Nov;16(11):1211-27
references.pmid: 15337521
references.citation: Gene. 2000 May 16;249(1-2):1-16
references.pmid: 10831834
references.citation: Neurobiol Dis. 2011 Aug;43(2):305-11
references.pmid: 21554955
references.citation: Nat Genet. 1995 May;10(1):3-4
references.pmid: 7647786
references.citation: BMC Dev Biol. 2007 Nov 15;7:127
references.pmid: 18005438
references.citation: J Biol Chem. 2009 Oct 23;284(43):29427-36
references.pmid: 19710014
references.citation: Exp Cell Res. 2008 Jun 10;314(10):1991-2003
references.pmid: 18456257