Abstract
Electrospray ionisation-ion mobility spectrometry–mass spectrometry (ESI-IMS–MS) is a powerful method for the study of conformational changes in protein complexes, including oligomeric species populated during protein self-aggregation into amyloid fibrils. Information on the mass, stability, cross-sectional area and ligand binding capability of each transiently populated intermediate, present in the heterogeneous mixture of assembling species, can be determined individually in a single experiment in real-time. Determining the structural characterisation of oligomeric species and alterations in self-assembly pathways observed in the presence of small molecule inhibitors is of great importance, given the urgent demand for effective therapeutics. Recent studies have demonstrated the capability of ESI-IMS–MS to identify small molecule modulators of amyloid assembly and to determine the mechanism by which they interact (positive, negative, non-specific binding, or colloidal) in a high-throughput format. Here, we demonstrate these advances using self-assembly of Aβ40 as an example, and reveal two new inhibitors of Aβ40 fibrillation.
Highlights
Amyloidosis contributes to more than 50 human disorders including Alzheimer’s disease (AD) [1], the most common form of dementia worldwide [2]
By exploiting the separative powers of ESI-IMS–MS, we first describe higher order oligomeric states populated by amyloid-b peptide residues 1–40 (Ab40), under conditions compatible both with ESI–MS and fibril formation, and elucidate their cross sectional areas (CCS)
Ab40 oligomer CCSs were estimated from the ESI-IMS–MS arrival time distributions and compared with CCSs estimated for theoretical oligomer growth models including a fit assuming isotropic growth [8], a fit assuming globular oligomers based on the average density of a protein under similar conditions
Summary
Amyloidosis contributes to more than 50 human disorders including Alzheimer’s disease (AD) [1], the most common form of dementia worldwide [2]. As the toxic species in many of these disorders remain elusive, current therapies focus on ameliorating symptoms, rather than preventing disease progression [4]. The identification and characterisation of the potentially toxic oligomers populated en route to amyloid fibrils is a significant challenge due to the heterogeneous, transient and lowly-populated nature of these species. When coupled to IMS, further separation of ions of the same m/z ratio but different collision-cross sectional areas (CCS) is enabled, allowing different conformational states of isobaric protein oligomers to be characterised simultaneously [5,9,10,11,12,13,14].
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