Identification of aspartic and isoaspartic acid residues in amyloid β peptides including Aβ 1-42 using electron-ion-reactions

摘要

Amyloid β peptides are the major components of the vascular and plaque amyloid filaments in individuals with Alzheimer’s disease (AD). Although it is still unclear what initiates the disease, isomerization of aspartic acid residues in Aβ peptides is directly related to the pathology of AD. The detection of isomerization products is analytically challenging due to their similar chemical properties and identical molecular mass. Different methods have been applied to differentiate and quantify the isomers, including immunology, chromatography and mass spectrometry. Typically, those methods require comparative analysis with the standard peptides and involve many sample preparation steps. To understand the role of Aβ isomerization in AD progression, a fast, simple, accurate, and reproducible method is necessary. In this work, Electron Capture Dissociation (ECD) Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR MS) was applied to detect isomerization in Aβ peptides. ECD generated diagnostic fragment ions for the two isomers of Aβ17-28: [M+2H-60]^•+ and z6^•-44 when aspartic acid and z6^•-57 when isoaspartic acid were present. Additionally, the zn-57 diagnostic ion was also observed in the Electron Ionization Dissociation (EID) spectra of the modified Aβ17-28 fragment. ECD was further applied towards Aβ1-40 and A1-β42. The diagnostic ion c6+57 was observed in the ECD spectra of the A1-β42 peptide demonstrating isomerization at residue 7. In conclusion, both ECD and EID can clearly determine the presence and the position of isoaspartic acid residues in Amyloid β peptides. The next step, therefore, is to apply this method to analyze samples of Alzheimer’s patients or healthy individuals in order to generate a better understanding of the disease.