Anti-PolyQ Antibodies Recognize a Short PolyQ Stretch in Both Normal and Mutant Huntingtin Exon 1

J Mol Biol. 2015 Jul 31;427(15):2507-2519. doi: 10.1016/j.jmb.2015.05.023. Epub 2015 Jun 3.


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.

Keywords: Huntington's disease; equilibrium gel-filtration; linear lattice; polyglutamine; small-angle X-ray scattering.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Antibodies, Monoclonal / immunology
  • Binding Sites / genetics
  • Chromatography, Gel
  • Drug Design
  • Epitopes / chemistry
  • Epitopes / genetics
  • Epitopes / immunology
  • Exons
  • Humans
  • Huntingtin Protein
  • Immunoglobulin Fab Fragments / chemistry
  • Immunoglobulin Fab Fragments / metabolism
  • Models, Molecular
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / immunology
  • Peptides / chemistry*
  • Peptides / genetics
  • Peptides / immunology
  • Protein Binding
  • Protein Conformation
  • Protein Multimerization


  • Antibodies, Monoclonal
  • Epitopes
  • HTT protein, human
  • Huntingtin Protein
  • Immunoglobulin Fab Fragments
  • Nerve Tissue Proteins
  • Peptides
  • polyglutamine