Development of a high-pH reversed-phase well plate for peptide fractionation and deep proteome analysis of cells and exosomes.

The complexity of the proteome often limits the number of identified proteins in the nanoflow LC-MS (nanoLC-MS) analysis of samples. Therefore, peptide fractionation is essential for reducing the sample complexity and improving the proteome coverage. In this study, to achieve high-pH reversed-phase (RP)-well plate fractionation for high-throughput proteomics analysis, C18 particles were coated on a 96-well plate, and the sample-loading processes were optimized for high-pH fractionation. The sample capacity of the high-pH RP-well plate was estimated to be ~6 μg of protein. There were 1.85- and 1.71-fold increases in the number of protein groups and peptides identified, respectively, with high-pH RP-well plate fractionation, compared to those without fractionation. In addition, with alkaline C18 well plate fractionation, exosome markers could be detected using ~1 μg of a protein digest of exosomes by microflow LC-MS (microLC-MS). These results illustrate that high-pH RP-well plate fractionation has superior sensitivity and effectiveness in preparing trace amounts of proteins for deep proteome analysis.