Probabilistic model applied to ion abundances in product-ion spectra: quantitative analysis of aspartic acid isomerization in peptides
Evaluation of post-translational modifications of protein molecules is important for both basic and applied biomedical research. Mass spectrometric quantitative studies of modifications, which do not change the mass of the protein, such as isomerization of aspartic acid, do not necessarily require the use of isotope-labelled standards. However, the accurate solution of this problem requires a deep understanding of the relationship between the mole fractions of the isomers and the peak intensities in the mass spectra. In previous studies on the isomerization of aspartic acid in short beta-amyloid fragments, it has been shown that calibration curves used for such quantitative studies often have a non-linear form. The reason for the deviation in the shape of the calibration curves from linearity has not yet been established. Here, we propose an explanation for this phenomenon based on a probabilistic model of the fragmentation process and present a general approach for the selection of fragments that can be used for quantitative studies of the degree of isomerization.
KeywordsMass spectrometry Label-free quantitation Isoaspartic acid Beta-amyloid peptides
The research was supported by the Russian Scientific Foundation Grant No. 16-14-00181.
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Conflict of interest
There authors declare that they have no conflicts of interest.
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