Pulsed hydrogen-deuterium exchange mass spectrometry probes conformational changes in amyloid beta (Aβ) peptide aggregation

Probing the conformational changes of amyloid beta (Aβ) peptide aggregation is challenging owing to the vast heterogeneity of the resulting soluble aggregates. To investigate the formation of these aggregates in solution, we designed an MS-based biophysical approach and applied it to the formation of soluble aggregates of the Aβ₄₂ peptide, the proposed causative agent in Alzheimer's disease. The approach incorporates pulsed hydrogen-deuterium exchange coupled with MS analysis. The combined approach provides evidence for a self-catalyzed aggregation with a lag phase, as observed previously by fluorescence methods. Unlike those approaches, pulsed hydrogen-deuterium exchange does not require modified Aβ₄₂ (e.g., labeling with a fluorophore). Furthermore, the approach reveals that the center region of Aβ₄₂ is first to aggregate, followed by the C and N termini. We also found that the lag phase in the aggregation of soluble species is affected by temperature and Cu²⁺ ions. This MS approach has sufficient structural resolution to allow interrogation of Aβ aggregation in physiologically relevant environments. This platform should be generally useful for investigating the aggregation of other amyloid-forming proteins and neurotoxic soluble peptide aggregates.