Fractionation of peptides and identification of proteins from Saccharomyces cerevisiae in proteomics with the use of reversed-phase capillary liquid chromatography and pI-based approach.

The aim of the work was to explore the identification of proteins from Saccharomyces cerevisiae using combined capillary reversed-phase liquid chromatography (RPLC) and in-solution isoelectric focusing (sIEF) for fractionation of peptides prior to mass spectrometry analysis. That method was proved to be the alternative separation method for complex mixtures of protein tryptic digests in proteomics. Analysis of the identification of peptides was performed with the use of electrospray ionization-ion trap tandem mass spectrometry (ESI-IT-MS/MS). First, the sIEF fractionation was carried out prior to separation and mass spectrometry identification by nano-LC/ESI-MS/MS instrument. The proposed approach based on sIEF and nano-LC/ESI-MS/MS analysis was proved to be an efficient and accurate alternative fractionation method of complex protein digests and can be considered as the useful tool for identification of proteins. Moreover, analytical information from that approach can be considered as the additional source of database matching constraint and can be valuable tool for analytical and bioinformatics studies of peptides fractionation in proteomics. Based on the MS/MS results obtained with ESI-IT-MS/MS instrument, 851 proteins from S. cerevisiae were identified. However, after careful analysis of the data reduction in number of proteins to 126 was obtained. Those results are discussed and interpreted in the view of the evaluation method used.