title: Anti-PolyQ Antibodies Recognize a Short PolyQ Stretch in Both Normal and Mutant Huntingtin Exon 1.
abstract: Huntington's disease is caused by expansion of a polyglutamine (polyQ) repeat in the huntingtin protein. A structural basis for the apparent transition between normal and disease-causing expanded polyQ repeats of huntingtin is unknown. The "linear lattice" model proposed random-coil structures for both normal and expanded polyQ in the preaggregation state. Consistent with this model, the affinity and stoichiometry of the anti-polyQ antibody MW1 increased with the number of glutamines. An opposing "structural toxic threshold" model proposed a conformational change above the pathogenic polyQ threshold resulting in a specific toxic conformation for expanded polyQ. Support for this model was provided by the anti-polyQ antibody 3B5H10, which was reported to specifically recognize a distinct pathologic conformation of soluble expanded polyQ. To distinguish between these models, we directly compared binding of MW1 and 3B5H10 to normal and expanded polyQ repeats within huntingtin exon 1 fusion proteins. We found similar binding characteristics for both antibodies. First, both antibodies bound to normal, as well as expanded, polyQ in huntingtin exon 1 fusion proteins. Second, an expanded polyQ tract contained multiple epitopes for fragments antigen-binding (Fabs) of both antibodies, demonstrating that 3B5H10 does not recognize a single epitope specific to expanded polyQ. Finally, small-angle X-ray scattering and dynamic light scattering revealed similar binding modes for MW1 and 3B5H10 Fab-huntingtin exon 1 complexes. Together, these results support the linear lattice model for polyQ binding proteins, suggesting that the hypothesized pathologic conformation of soluble expanded polyQ is not a valid target for drug design.
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; Graduate Option in Biochemistry and Molecular Biophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Gwen E
authors.initials: GE
authors.lastname: Owens
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Danielle M
authors.initials: DM
authors.lastname: New
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: West
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, MD 20815-6789, USA. Electronic address: bjorkman@caltech.edu.
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Bjorkman
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites / Q000235:genetics; D002850:Chromatography, Gel; D015195:Drug Design; D000939:Epitopes / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D005091:Exons; D006801:Humans; D000071058:Huntingtin Protein; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; C086055:HTT protein, human; D000071058:Huntingtin Protein; D007140:Immunoglobulin Fab Fragments; D009419:Nerve Tissue Proteins; D010455:Peptides; C097188:polyglutamine
keywords: Huntington's disease; equilibrium gel-filtration; linear lattice; polyglutamine; small-angle X-ray scattering