ABSTRACT
Amyloid beta (Aß) proteins are produced from amyloid precursor protein cleaved by ß- and γ-secretases, and are the main components of senile plaques pathologically found in Alzheimer's disease (AD) patient brains. Therefore, the relationship between AD and Aßs has been well studied for both therapeutic and diagnostic purposes. Several enzymes have been reported to degrade Aßs in vivo, with neprilysin (NEP) and insulysin (insulin-degrading enzyme, IDE) being the most prominent. In this article, we describe the mass spectrometric characterization of peptide fragments generated using NEP and IDE, and clarify the differences in digestion specificities between these two enzymes for non-aggregated Aß40, aggregated Aß40, and Aß40 peptide fragments, including Aß16. Our results allowed identification of all the peptide fragments from non-aggregated Aß40: NEP, 23 peptide fragments consisting of 2-11 amino-acid residues, 17 cleavage sites; IDE, 23 peptide fragments consisting of 6-33 amino-acid residues, 15 cleavage sites. Also, we confirmed that IDE can digest only whole Aß40, whereas NEP can digest both Aß40 and partial structures such as Aß16 and peptide fragments generated by the digestion of Aß40 by IDE. Furthermore, we confirmed that IDE and NEP are unable to digest aggregated Aß40.
