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Distribution of isomerized and racemized amyloid β isoforms in sporadic Alzheimer’s disease using ion‐mobility mass spectrometry

Extracellular amyloid plaques and intracellular neurofibrillary tangles are the pathological hallmarks of Alzheimer’s Disease (AD). It takes on average 19 years for amyloid β (Aβ) peptides to deposit as insoluble plaques from onset to clinical dementia symptoms in AD. Such long‐lived nature of amyloidosis predisposes the polypeptide chains to undergo multiple spontaneous and non‐enzymatic post‐translational modifications (PTMs), which can render them resistant to normal cellular proteolysis mechanisms. Several biochemical approaches have estimated very high degree of isomerization and racemization of Asp and Ser residues in Aβ purified from the insoluble plaques. This goes along with a sequential loss of N‐terminal amino acids. However, comprehensive characterisation of these isomers as well as their quantitative estimation is yet to be done.