Synthetic ß-sheets mimicking fibrillar and oligomeric structures for evaluation of spectral X-ray scattering technique for biomarker quantification.

ABSTRACT

BACKGROUND: Archetypical cross-ß spines sharpen the boundary between functional and pathological proteins including ß-amyloid, tau, α-synuclein and transthyretin are linked to many debilitating human neurodegenerative and non-neurodegenerative amyloidoses. An increased focus on development of pathogenic ß-sheet specific fluid and imaging structural biomarkers and conformation-specific monoclonal antibodies in targeted therapies has been recently observed. Identification and quantification of pathogenic oligomers remain challenging for existing neuroimaging modalities. RESULTS: We propose two artificial ß-sheets which can mimic the nanoscopic structural characteristics of pathogenic oligomers and fibrils for evaluating the performance of a label free, X-ray based biomarker detection and quantification technique. Highly similar structure with elliptical cross-section and parallel cross-ß motif is observed among recombinant α-synuclein fibril, Aß-42 fibril and artificial ß-sheet fibrils. We then use these ß-sheet models to assess the performance of spectral small angle X-ray scattering (sSAXS) technique for detecting ß-sheet structures. sSAXS showed quantitatively accurate detection of antiparallel, cross-ß artificial oligomers from a tissue mimicking environment and significant distinction between different oligomer packing densities such as diffuse and dense packings. CONCLUSION: The proposed synthetic ß-sheet models mimicked the nanoscopic structural characteristics of ß-sheets of fibrillar and oligomeric states of Aß and α-synuclein based on the ATR-FTIR and SAXS data. The tunability of ß-sheet proportions and shapes of structural motifs, and the low-cost of these ß-sheet models can become useful test materials for evaluating ß-sheet or amyloid specific biomarkers in a wide range of neurological diseases. By using the proposed synthetic ß-sheet models, our study indicates that the sSAXS has potential to evaluate different stages of ß-sheet-enriched structures including oligomers of pathogenic proteins.