Branching in Amyloid Fibril Growth |
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Authors: | Christian Beyschau Andersen Hisashi Yagi Vincenzo Martorana Gunna Christiansen Yuji Goto |
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Affiliation: | † Protein Structure and Biophysics, Novo Nordisk A/S, DK-2760 Måløv, Denmark ‡ Department of Life Sciences, Aalborg University, DK-9000 Aalborg, Denmark § Institute for Protein Research, Osaka University and CREST, Japan Science and Technology Agency, Osaka 565-0871, Japan ¶ Institute of Biophysics, National Research Council, I-90146 Palermo, Italy ⊥ Institute of Medical Microbiology and Immunology, University of Aarhus, DK-8000 Århus C, Denmark ∗∗ Centre for insoluble Protein Structures (inSPIN), Center for Interdisciplinary Nanoscience (INANO), Department of Molecular Biology, University of Aarhus, DK-8000 Århus C, Denmark |
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Abstract: | Using the peptide hormone glucagon and Aβ(1-40) as model systems, we have sought to elucidate the mechanisms by which fibrils grow and multiply. We here present real-time observations of growing fibrils at a single-fibril level. Growing from preformed seeds, glucagon fibrils were able to generate new fibril ends by continuously branching into new fibrils. To our knowledge, this is the first time amyloid fibril branching has been observed in real-time. Glucagon fibrils formed by branching always grew in the forward direction of the parent fibril with a preferred angle of 35-40°. Furthermore, branching never occurred at the tip of the parent fibril. In contrast, in a previous study by some of us, Aβ(1-40) fibrils grew exclusively by elongation of preformed seeds. Fibrillation kinetics in bulk solution were characterized by light scattering. A growth process with branching, or other processes that generate new ends from existing fibrils, should theoretically give rise to different fibrillation kinetics than growth without such a process. We show that the effect of adding seeds should be particularly different in the two cases. Our light-scattering data on glucagon and Aβ(1-40) confirm this theoretical prediction, demonstrating the central role of fibril-dependent nucleation in amyloid fibril growth |
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Keywords: | Aβ(1-40), amyloid β-peptide residue 1-40 TIRFM, total internal reflection fluorescence microscopy SALS, small-angle light scattering LALS, large-angle light scattering AFM, atomic force microscopy IAPP, islet amyloid polypeptide TEM, transmission electron microscopy |
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