The N-domain of angiotensin-converting enzyme specifically hydrolyzes the Arg-5-His-6 bond of Alzheimer's Aβ-(1-16) peptide and its isoAsp-7 analogue with different efficiency as evidenced by quantitative matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Chronic imbalance between production and degradation of the human amyloid-beta peptide (A beta) is assumed to play an important role in pathogenesis of Alzheimer's disease (AD). Post-translational modifications of A beta could influence its interactions with specifically cleaving proteases and, therefore, perturb the A beta homeostasis. The angiotensin-converting enzyme (ACE) was previously shown to degrade non-modified A beta in vitro and in cells. In the presented work, we investigated the effect of isomerization of Asp-7, a common non-enzymatic age-related modification found in AD-associated A beta species, on hydrolysis of A beta by ACE. Two synthetic peptides corresponding to the A beta region 1-16 with either Asp or isoAsp residues in position 7 were examined as monomeric soluble substrates for the N- as well as for the C-domain of ACE. The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) coupled with the O-18-labeled internal standard approach has allowed us to show that (i) the N-domain of ACE (N-ACE), but not the C-domain, selectively cleaves the Arg-5-His-6 bond in both peptides, and that GO N-ACE hydrolyzes the isoAsp-7 analogue more efficiently than the non-modified one. Our results demonstrate a new endopeptidase activity of N-ACE as well as high preference of the domain to recognize and hydrolyze the isomerized A beta species that were earlier suggested to promote AD pathogenesis. The results suggest the need for further analysis of biological effects of isomerized A beta and its interaction with ACE in AD pathogenesis. Copyright (c) 2007 John Wiley & Sons, Ltd.