Hydrolysis of the amyloid β-peptide (Aβ) 1-40 between Asp23-Val24 produces non-aggregating fragments.: An electrospray mass spectrometric study

The aggregation of full-length (residues 1-40) amyloid p-peptide (Abeta) and fragments corresponding to residues 1-23 and 24-40 was studied by electrospray mass spectrometry, using gramicidin as a non-aggregating reference. Following a lag period, Abeta(1-40) at 140 pm concentration aggregates with apparent first-order kinetics. Under acidic conditions Abeta(1-40) undergoes spontaneous cleavage between Asp23-Val24 and to a lesser extent also at two other Asp-X motifs. Incubation in acidic (H2O)-O-18 showed incorporation of O-18 in fragment Abeta(1-23), confirming that the Asp23-Val24 peptide bond had been hydrolyzed. Incubation of synthetic Abeta(1-23) and Abeta(24-40) peptides with Abeta(1-40) showed that Abeta(24-40) remained in solution for several months, that Abeta(1-23) partly disappeared from solution, whereas Abeta(1-40) completely disappeared. Further, treatment of sedimentable aggregates formed after co-incubation of the three peptides with hexafluoro-2-propanol or formic acid recovered the intensity of Abeta(1-40). These data support previous studies showing that the region of Abeta encompassing residues 16-24 is necessary for aggregation into amyloid fibrils. Copyright (C) 2005 John Wiley Sons, Ltd.