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An Improved Scoring Method for the Identification of Endogenous Peptides based on Mascot MS/MS Ion Search

An Improved Scoring Method for the Identification of Endogenous Peptides based on Mascot MS/MS Ion Search image
An Improved Scoring Method for the Identification of Endogenous Peptides based on Mascot MS/MS Ion Search image
To identify the endogenous peptides using MS/MS analysis and searching against a polypeptide sequence database, a non-enzyme specific (NES) search considering all of the possible proteolytic cleavages is required. However, the use of a NES search generates more false positive hits than an enzyme specific search, and therefore has lower identification performance. In this study, the use of the sub-ranked matches for improving the identification performance of Mascot NES search was investigated and a new scoring method was developed that considered the contribution of all sub-ranked random match probabilities, named contribution score (CS). The CS showed the highest identification sensitivity using Mascot NES search with a full protein database when compared to the use of the Mascot first ranked score and delta score (DS). The confident peptides identified by DS and CS were showed to be complementary. When applied to plant endogenous peptide identification, the identification numbers of tomato endogenous peptides using DS and CS were 176.3% and 184.2%, respectively, higher than the use of the first ranked score of Mascot. The combination of DS and CS identified 200.0% and 8.6% more tomato endogenous peptides than the use of Mascot and DS, respectively. This method by combining the CS and DS can significantly improve the identification performance of endogenous peptides without complex computational steps and is also able to improve the identification performance of enzyme specific search. In addition to the application on the plant peptidomics analysis, this method may be applied to the improvement of peptidomics studies in different species. A web interface for calculating the DS and CS based on Mascot search results was developed herein.

Ying-Lan Chen, Wei-Hung Chang, Chi-Ying Lee and Yet-Ran Chen * (2019) An Improved Scoring Method for the Identification of Endogenous Peptides based on Mascot MS/MS Ion Search Analyst, 144(9):3045-3055