Force spectroscopy reveals the presence of structurally modified dimers in transthyretin amyloid annular oligomers.
Toxicity in amyloidogenic protein misfolding disorders is thought to involve intermediate states of aggregation associated with the formation of amyloid fibrils. Despite their relevance, the heterogeneity and transience of these oligomers have placed great barriers in our understanding of their structural properties. Among amyloid intermediates, annular oligomers or annular protofibrils have raised considerable interest because they may contribute to a mechanism of cellular toxicity via membrane permeation. Here we investigated, by using AFM force spectroscopy, the structural detail of amyloid annular oligomers from transthyretin (TTR), a protein involved in systemic and neurodegenerative amyloidogenic disorders. Manipulation was performed in situ, in the absence of molecular handles and using persistence length-fit values to select relevant curves. Force curves reveal the presence of dimers in TTR annular oligomers that unfold via a series of structural intermediates. This is in contrast with the manipulation of native TTR that was more often manipulated over length scales compatible with a TTR monomer and without unfolding intermediates. Imaging and force spectroscopy data suggest that dimers are formed by the assembly of monomers in a head-to-head orientation with a nonnative interface along their β-strands. Furthermore, these dimers stack through nonnative contacts that may enhance the stability of the misfolded structure.
Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary.|Institute for Molecular and Cell Biology (IBMC), Porto, Portugal.
Ricardo H
0000-0003-4959-7576
RH
Pires
Institute for Molecular and Cell Biology (IBMC), Porto, Portugal.|Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, Porto, Portugal.
Maria J
MJ
Saraiva
Institute for Molecular and Cell Biology (IBMC), Porto, Portugal.|Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, Porto, Portugal.
Ana M
AM
Damas
Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary.|MTA-SE Molecular Biophysics Research Group, Budapest, Hungary.
Miklós S Z
MS
Kellermayer
D000682:Amyloid / Q000737:chemistry*; D019281:Dimerization; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force / Q000379:methods*; D008958:Models, Molecular; D011228:Prealbumin / Q000737:chemistry*; D017433:Protein Structure, Secondary; D058767:Protein Unfolding; D013054:Spectrophotometry, Atomic / Q000379:methods*
D000682:Amyloid; D011228:Prealbumin; C076571:transthyretin-related amyloid fibril protein, human
amyloid; annular oligomers; annular protofibrils; atomic force microscopy; force spectroscopy; transthyretin