title: Inhibiting the nucleation of amyloid structure in a huntingtin fragment by targeting α-helix-rich oligomeric intermediates.
abstract: Although oligomeric intermediates are transiently formed in almost all known amyloid assembly reactions, their mechanistic roles are poorly understood. Recently, we demonstrated a critical role for the 17-amino-acid N-terminus (htt(NT) segment) of huntingtin (htt) in the oligomer-mediated amyloid assembly of htt N-terminal fragments. In this mechanism, the htt(NT) segment forms the α-helix-rich core of the oligomers, leaving much of the polyglutamine (polyQ) segment disordered and solvent-exposed. Nucleation of amyloid structure occurs within this local high concentration of disordered polyQ. Here we demonstrate the kinetic importance of htt(NT) self-assembly by describing inhibitory htt(NT)-containing peptides that appear to work by targeting nucleation within the oligomer fraction. These molecules inhibit amyloid nucleation by forming mixed oligomers with the htt(NT) domains of polyQ-containing htt N-terminal fragments. In one class of inhibitors, nucleation is passively suppressed due to the reduced local concentration of polyQ within the mixed oligomer. In the other class, nucleation is actively suppressed by a proline-rich polyQ segment covalently attached to htt(NT). Studies with D-amino acid and scrambled sequence versions of htt(NT) suggest that inhibition activity is strongly linked to the propensity of inhibitory peptides to make amphipathic α-helices. Htt(NT) derivatives with C-terminal cell-penetrating peptide segments also exhibit excellent inhibitory activity. The htt(NT)-based peptides described here, especially those with protease-resistant d-amino acids and/or with cell-penetrating sequences, may prove useful as lead therapeutics for inhibiting the nucleation of amyloid formation in Huntington's disease.
authors.affiliation: Department of Structural Biology and Pittsburgh Institute for Neurodegenerative Disease, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Mishra
authors.forename: Murali
authors.initials: M
authors.lastname: Jayaraman
authors.forename: Bartholomew P
authors.initials: BP
authors.lastname: Roland
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Landrum
authors.forename: Timothy
authors.initials: T
authors.lastname: Fullam
authors.forename: Ravindra
authors.initials: R
authors.lastname: Kodali
authors.forename: Ashwani K
authors.initials: AK
authors.lastname: Thakur
authors.forename: Irene
authors.initials: I
authors.lastname: Arduini
authors.forename: Ronald
authors.initials: R
authors.lastname: Wetzel
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000682:Amyloid / Q000037:antagonists & inhibitors / Q000138:chemical synthesis* / Q000235:genetics; D045744:Cell Line, Tumor; D057846:Cell-Penetrating Peptides / Q000737:chemistry; D006801:Humans; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000138:chemical synthesis* / Q000235:genetics; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000138:chemical synthesis* / Q000235:genetics; D010455:Peptides / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis*; D017433:Protein Structure, Secondary
chemical_list: D000596:Amino Acids; D000682:Amyloid; D057846:Cell-Penetrating Peptides; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011108:Polymers; C097188:polyglutamine