Inhibiting the nucleation of amyloid structure in a huntingtin fragment by targeting α-helix-rich oligomeric intermediates

摘要

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.