title: A mass spectrometric approach for characterization of amyloid-β aggregates and identification of their post-translational modifications.
abstract: Endogenous amyloid-β (Aβ) oligomeric aggregates have been proposed as toxic agents in Alzheimer's disease (AD). Knowledge of their structures not only may provide insight into the basis of their neurotoxicities but also may reveal new targets for therapeutic drugs and diagnostic tools. However, the low levels of these Aβ oligomers have impeded structural characterization. Evidence suggests that the endogenous oligomers are covalently modified in vivo. In this report, we demonstrate an established mass spectrometry (MS) methodology called precursor ion mapping (PIM) that potentially may be applied to endogenous oligomer characterization. First, we illustrate the use of this PIM technique with a synthetic Aβ(1-40) monomer sample that had been cross-linked with transglutaminase (TGase) and digested with pepsin. From PIM analysis of an Aβ(4-13) MS/MS fragment, precursor ions were identified that corresponded to peptic fragments of three TGase cross-linked species: Aβ(4-19)--(4-19), Aβ(4-19)--(20-34), and Aβ(1-19)--(20-34). Next, we demonstrate the applicability of the PIM technique to an endogenous Aβ sample that had been purified and concentrated by immunoaffinity chromatography. Without pepsin digestion, we successfully identified the full length and C-terminally truncated monomeric Aβ species 1-35 to 1-42, along with select methionine-oxidized counterparts. Because PIM focuses only on a subpopulation of ions, namely the related precursor ions, the resulting spectra are of increased specificity and sensitivity. Therefore, this methodology shows great promise for structural analysis and identification of post-translational modification(s) in endogenous Aβ oligomers.
authors.affiliation: Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, Florida 32224, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Tay
authors.forename: Jennifer G
authors.initials: JG
authors.lastname: Bryant
authors.forename: Patricia K
authors.initials: PK
authors.lastname: Martin
authors.forename: A Jeremy
authors.initials: AJ
authors.lastname: Nix
authors.forename: Bernadette M
authors.initials: BM
authors.lastname: Cusack
authors.forename: Terrone L
authors.initials: TL
authors.lastname: Rosenberry
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D013058:Mass Spectrometry; D010434:Pepsin A / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D021241:Spectrometry, Mass, Electrospray Ionization; D011503:Transglutaminases / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); D011503:Transglutaminases; D010434:Pepsin A