Protein glycosylation plays fundamental roles in many cellular processes, and previous reports have shown dysregulation to be associated with several human diseases, including diabetes, cancer, and neurodegenerative disorders. Despite the vital role of glycosylation for proper protein function, the analysis of glycoproteins has been lagged behind to other protein modifications. In this study, we describe the re-analysis of global proteomic data from breast cancer xenograft tissues using recently developed software package GPQuest 2.0, revealing a large number of previously unidentified N-linked glycopeptides. More importantly, we found that using immobilized metal affinity chromatography (IMAC) technology for the enrichment of phosphopeptides had coenriched a substantial number of sialoglycopeptides, allowing for a large-scale analysis of sialoglycopeptides in conjunction with the analysis of phosphopeptides. Collectively, combined MS/MS analyses of global proteomic and phosphoproteomic datasets resulted in the identification of 6,724 N-linked glycopeptides from 617 glycoproteins derived from two breast cancer xenograft tissues. Next, we utilized GPQuest for the re-analysis of global and phosphoproteomic data generated from 108 human breast cancer tissues that were previously analyzed by Clinical Proteomic Analysis Consortium (CPTAC). Reanalysis of the CPTAC dataset resulted in the identification of 2,683 glycopeptides from the global proteomic data set and 4,554 glycopeptides from phosphoproteomic data set, respectively. Together, 11,292 N-linked glycopeptides corresponding to 1,731 N-linked glycosites from 883 human glycoproteins were identified from the two data sets. This analysis revealed an extensive number of glycopeptides hidden in the global and enriched in IMAC-based phosphopeptide-enriched proteomic data, information which would have remained unknown from the original study otherwise. The reanalysis described herein can be readily applied to identify glycopeptides from already existing data sets, providing insight into many important facets of protein glycosylation in different biological, physiological, and pathological processes.would not contain the sialic residue. Further investigation of the influence of IMAC-enrichment on intact glycopeptides, specifically sialylated intact glycopeptides is warranted, as well as the scheme of the co-enrichment of both phosphopeptides and intact glycopeptides.
ConclusionsWith the rapid development of mass spectrometry and computational glycoproteomics tools, we can conduct a large-scale analysis of glycoproteome without specific glycopeptide enrichment and mass spectrometry analysis. In this study, we used our recently developed and improved intact glycopeptide analysis tool, GPQuest 2.0, to investigate the glycopeptide expression in two large datasets: two breast cancer xenograft samples and 108 CPTAC breast cancer tissues. The search results of 'oxo-spectra' and intact N-linked glycopeptides analysis demonstrated the feasibility of profiling glycoproteome utiliz...