Label-Free Phosphoproteomics Profiling of Fission Yeast Schizosaccharomyces pombe

The phosphorylation of proteins modulates various functions of proteins and plays an important role in regulation of cell signaling. In the recent years, the label-free quantitative (LFQ) phos-phoproteomics has become the powerful tool to analyze the phosphorylation of proteins within the complex samples. Despite the great progress, the studies of protein phosphorylations are still limited in throughput, robustness, and reproducibility, hampering analyses that involve multiple perturbations, such as those needed to follow the dynamics of phosphoproteomes. To address these challenges, we introduce here the LFQ phosphoproteomics workflow that is based on Fe-IMAC phosphopeptide enrichment followed by strong anion exchange (SAX) and porous graphitic carbon (PGC) fractionation strategies. We applied this workflow to analyze the whole-cell phosphoproteome of the fission yeast Schizosaccharomyces pombe. Using the strategy, we identified 8353 phosphosites from which 1274 were newly identified. This provides the sig-nificant addition to the S. pombe phosphoproteome. Results of our study highlight that combining of PGC and SAX fractionation strategies substantially increases the robustness and specificity of LFQ phosphoproteomics. Overall, the presented LFQ phosphoproteomics workflow opens the door for studies that would get better insight into the complexity of the protein kinase functions of the fission yeast S. pombe.