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Open Access Methodology article

Optimal precursor ion selection for LC-MALDI MS/MS

Alexandra Zerck1*, Eckhard Nordhoff12, Hans Lehrach1 and Knut Reinert3

Author affiliations

1 Department of Vertebrate Genomics, Max Planck Institute for Molecular Genetics, Ihnestr. 63-73, Berlin, 14195, Germany

2 , Current address: M2-Automation, Berlin, Germany

3 Department of Computer Science, Free University Berlin, Takustr. 9, Berlin, 14195, Germany

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Citation and License

BMC Bioinformatics 2013, 14:56  doi:10.1186/1471-2105-14-56

Published: 18 February 2013

Abstract

Background

Liquid chromatography mass spectrometry (LC-MS) maps in shotgun proteomics are often too complex to select every detected peptide signal for fragmentation by tandem mass spectrometry (MS/MS). Standard methods for precursor ion selection, commonly based on data dependent acquisition, select highly abundant peptide signals in each spectrum. However, these approaches produce redundant information and are biased towards high-abundance proteins.

Results

We present two algorithms for inclusion list creation that formulate precursor ion selection as an optimization problem. Given an LC-MS map, the first approach maximizes the number of selected precursors given constraints such as a limited number of acquisitions per RT fraction. Second, we introduce a protein sequence-based inclusion list that can be used to monitor proteins of interest. Given only the protein sequences, we create an inclusion list that optimally covers the whole protein set. Additionally, we propose an iterative precursor ion selection that aims at reducing the redundancy obtained with data dependent LC-MS/MS. We overcome the risk of erroneous assignments by including methods for retention time and proteotypicity predictions. We show that our method identifies a set of proteins requiring fewer precursors than standard approaches. Thus, it is well suited for precursor ion selection in experiments with limited sample amount or analysis time.

Conclusions

We present three approaches to precursor ion selection with LC-MALDI MS/MS. Using a well-defined protein standard and a complex human cell lysate, we demonstrate that our methods outperform standard approaches. Our algorithms are implemented as part of OpenMS and are available under http://www.openms.de webcite.