Adjacent Y-Ion Ratio Distributions and Its Application in Peptide Sequencing

A scoring function plays a critical role in software for peptide identification with mass spectrometry. We present a general scoring feature that can be incorporated in the scoring functions of other peptide identification software. The scoring feature is based on the intensity ratios between two adjacent y-ions in the spectrum. A method is proposed to obtain the probability distributions of such ratios, and to calculate the scoring feature based on the distributions. To demonstrate the performance of the method, the new feature is incorporated with X!Tandem [1] , [2] and Novor [3] and significantly improved the database search and de novo sequencing performances on the testing data, respectively.