Simultaneous Quantification of Protein Phosphorylation Sites using Liquid Chromatography鈥揟andem Mass Spectrometry-Based Targeted Proteomics: A Linear Algebra Approach for Isobaric Phosphopeptides
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- 作者：Feifei Xu ; Ting Yang ; Yuan Sheng ; Ting Zhong ; Mi Yang ; Yun Chen
- 刊名：Journal of Proteome Research
- 出版年：2014
- 出版时间：December 5, 2014
- 年：2014
- 卷：13
- 期：12
- 页码：5452-5460
- 全文大小：346K
- ISSN：1535-3907
文摘
As one of the most studied post-translational modifications (PTM), protein phosphorylation plays an essential role in almost all cellular processes. Current methods are able to predict and determine thousands of phosphorylation sites, whereas stoichiometric quantification of these sites is still challenging. Liquid chromatography coupled with tandem mass spectrometry (LC鈥揗S/MS)-based targeted proteomics is emerging as a promising technique for site-specific quantification of protein phosphorylation using proteolytic peptides as surrogates of proteins. However, several issues may limit its application, one of which relates to the phosphopeptides with different phosphorylation sites and the same mass (i.e., isobaric phosphopeptides). While employment of site-specific product ions allows for these isobaric phosphopeptides to be distinguished and quantified, site-specific product ions are often absent or weak in tandem mass spectra. In this study, linear algebra algorithms were employed as an add-on to targeted proteomics to retrieve information on individual phosphopeptides from their common spectra. To achieve this simultaneous quantification, a LC鈥揗S/MS-based targeted proteomics assay was first developed and validated for each phosphopeptide. Given the slope and intercept of calibration curves of phosphopeptides in each transition, linear algebraic equations were developed. Using a series of mock mixtures prepared with varying concentrations of each phosphopeptide, the reliability of the approach to quantify isobaric phosphopeptides containing multiple phosphorylation sites (鈮?) was discussed. Finally, we applied this approach to determine the phosphorylation stoichiometry of heat shock protein 27 (HSP27) at Ser78 and Ser82 in breast cancer cells and tissue samples.