High-resolution separation of amyloid beta-peptides: structural variants present in Alzheimer's disease amyloid.

In Alzheimer's disease (AD), one of the cardinal neuropathological signs is deposition of amyloid, primarily consisting of the amyloid beta-peptide (Abeta). Structural variants of AD-associated Abeta peptides have been difficult to purify by high-resolution chromatographic techniques. We therefore developed a novel chromatographic protocol, enabling high-resolution reverse-phase liquid chromatography (RPLC) purification of Abeta variants displaying very small structural differences. By using a combination of size-exclusion chromatography and the novel RPLC protocol, Abeta peptides extracted from AD amyloid were purified and subsequently characterized. Structural analysis by microsequencing and electrospray-ionization mass spectrometry revealed that the RPLC system resolved a complex mixture of Abeta variants terminating at either residue 40 or 42. Abeta variants differing by as little as one amino acid residue could be purified rapidly to apparent homogeneity. The resolution of the system was further illustrated by its ability to separate the structural isomers of Abeta1-40. The present chromatography system might provide further insight into the role of N-terminally and posttranslationally modified Abeta variants, because each variant can now be studied individually.