title: Super-resolution fluorescence of huntingtin reveals growth of globular species into short fibers and coexistence of distinct aggregates.
abstract: Polyglutamine-expanded huntingtin, the protein encoded by HTT mutations associated with Huntington's disease, forms aggregate species in vitro and in vivo. Elucidation of the mechanism of growth of fibrillar aggregates from soluble monomeric protein is critical to understanding the progression of Huntington's disease and to designing therapeutics for the disease, as well as for aggregates implicated in Alzheimer's and Parkinson's diseases. We used the technique of multicolor single-molecule, super-resolution fluorescence imaging to characterize the growth of huntingtin exon 1 aggregates. The huntingtin exon 1 aggregation followed a pathway from exclusively spherical or globular species of ∼80 nm to fibers ∼1 μm in length that increased in width, but not length, over time with the addition of more huntingtin monomers. The fibers further aggregated with one another into aggregate assemblies of increasing size. Seeds created by sonication, which were comparable in shape and size to the globular species in the pathway, were observed to grow through multidirectional elongation into fibers, suggesting a mechanism for growth of globular species into fibers. The single-molecule sensitivity of our approach made it possible to characterize the aggregation pathway across a large range of size scales, from monomers to fiber assemblies, and revealed the coexistence of different aggregate species (globular species, fibers, fiber assemblies) even at late time points.
authors.affiliation: Department of Chemistry, ‡Department of Applied Physics, and §Department of Biology, Stanford University , Stanford, California 94305, United States.
authors.forename: Whitney C
authors.initials: WC
authors.lastname: Duim
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Koning
authors.initials: K
authors.lastname: Shen
authors.forename: Judith
authors.initials: J
authors.lastname: Frydman
authors.forename: W E
authors.initials: WE
authors.lastname: Moerner
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005091:Exons; D015870:Gene Expression; D006801:Humans; D000071058:Huntingtin Protein; D057054:Molecular Imaging; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D066329:Protein Aggregates; D011487:Protein Conformation; D055503:Protein Multimerization; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013010:Sonication; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013997:Time Factors
chemical_list: C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D066329:Protein Aggregates; D011993:Recombinant Fusion Proteins