Rapid characterization of amyloid-beta side-chain oxidation by tandem mass spectrometry and the scoring algorithm for spectral analysis.
OBJECTIVE
Amyloid-beta (Abeta) is a self-aggregating protein found in senile plaques in Alzheimer's disease (AD) brain and is thought to play a major role in the disease process. Oxidative stress may be a predominant cause of the formation of these Abeta aggregates. This study aims at identifying possible sites of copper-catalyzed oxidation of Abeta1-40 using liquid chromatography tandem mass spectrometry (LC/MS/MS) and scoring algorithm for spectral analysis (SALSA). Traditionally, identification of post-translational modifications by tandem mass spectrometric analysis requires users to inspect manually thousands of MS/MS spectra, which can be a tedious and time-consuming process. With the use of SALSA, users can automatically search for post-translational modifications based on the spacing of the m/z values associated with the ion series of an amino acid sequence.


METHODS
Abeta1-40 was subjected to copper-catalyzed oxidative stress. LC/MS/MS and SALSA analyses were used to determine the sites of post-translational modification within the tryptic fragments.


RESULTS
Oxidation was found to occur preferentially at the histidine residues Hisl3 and Hisl4 and at the methionine residue (Met35) of Abeta1-40.


CONCLUSIONS
The combination of LC/MS/MS and SALSA searches could dramatically improve the efficiency and accuracy of determining the specific sites of oxidation of in vitro, copper-oxidized Abeta1-40 as well as other oxidized proteins.
Schiewe
Alexandra J
AJ
Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, California, USA.
Margol
Lawrence
L
Soreghan
Brian A
BA
Thomas
Stefani N
SN
Yang
Austin J
AJ
D000465:Algorithms; D016229:Amyloid beta-Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D002853:Chromatography, Liquid / Q000379:methods; D003300:Copper; D013058:Mass Spectrometry / Q000379:methods; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry*
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); D003300:Copper