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Is supramolecular filament chirality the underlying cause of major morphology differences in amyloid fibrils?

ABSTRACT: The unique enhanced sensitivity of vibrational circular dichroism (VCD) to the formation and development of amyloid fibrils in solution is extended to four additional fibril-forming proteins or peptides where it is shown that the sign of the fibril VCD pattern correlates with the sense of supramolecular filament chirality and, without exception, to the dominant fibril morphology as observed in AFM or SEM images. Previously for insulin, it has been demonstrated that the sign of the VCD band pattern from filament chirality can be controlled by adjusting the pH of the incubating solution, above pH 2 for "normal" left-hand-helical filaments and below pH 2 for "reversed" right-hand-helical filaments. From AFM or SEM images, left-helical filaments form multifilament braids of left-twisted fibrils while the right-helical filaments form parallel filament rows of fibrils with a flat tape-like morphology, the two major classes of fibril morphology that from deep UV resonance Raman scattering exhibit the same cross-β-core secondary structure. Here we investigate whether fibril supramolecular chirality is the underlying cause of the major morphology differences in all amyloid fibrils by showing that the morphology (twisted versus flat) of fibrils of lysozyme, apo-α-lactalbumin, HET-s (218-289) prion, and a short polypeptide fragment of transthyretin, TTR (105-115), directly correlates to their supramolecular chirality as revealed by VCD. The result is strong evidence that the chiral supramolecular organization of filaments is the principal underlying cause of the morphological heterogeneity of amyloid fibrils. Because fibril morphology is linked to cell toxicity, the chirality of amyloid aggregates should be explored in the widely used in vitro models of amyloid-associated diseases.

SUBMITTER: Kurouski D

PROVIDER: S-EPMC3968177 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundBeside neurofibrillary tangles, amyloid plaques are the major histological hallmarks of Alzheimer's disease (AD) being composed of aggregated fibrils of β-amyloid (Aβ). During the underlying fibrillogenic pathway, starting from a surplus of soluble Aβ and leading to mature fibrils, multiple conformations of this peptide appear, including oligomers of various shapes and sizes. To further investigate the fibrillization of β-amyloid and to have tools at hand to monitor the distribution of aggregates in the brain or even act as disease modulators, it is essential to develop highly sensitive antibodies that can discriminate between diverse aggregates of Aβ.ResultsHere we report the generation and characterization of a variety of amyloid-β specific human and human-like antibodies. Distinct fractions of monomers and oligomers of various sizes were separated by size exclusion chromatography (SEC) from Aβ42 peptides. These antigens were used for the generation of two Aβ42 specific immune scFv phage display libraries from macaque (Macaca fascicularis). Screening of these libraries as well as two naïve human phage display libraries resulted in multiple unique binders specific for amyloid-β. Three of the obtained antibodies target the N-terminal part of Aβ42 although with varying epitopes, while another scFv binds to the α-helical central region of the peptide. The affinities of the antibodies to various Aβ42 aggregates as well as their ability to interfere with fibril formation and disaggregation of preformed fibrils were determined. Most significantly, one of the scFv is fibril-specific and can discriminate between two different fibril forms resulting from variations in the acidity of the milieu during fibrillogenesis.ConclusionWe demonstrated that the approach of animal immunization and subsequent phage display based antibody selection is applicable to generate highly specific anti β-amyloid scFvs that are capable of accurately discriminating between minute conformational differences.

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Is supramolecular filament chirality the underlying cause of major morphology differences in amyloid fibrils?

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