Biomarker Discovery via N-Glycoproteomics.

Posttranslational modifications (PTMs) of proteins regulate several biological processes, and investigating their diversity is crucial for understanding the mechanisms of cell regulation. Glycosylation is one of the most complex posttranslational modifications that control fundamental cellular processes such as protein folding, protein trafficking, host-pathogen interactions, cell adhesion, and cytokine receptor signaling networks. N-linked glycosylation denotes the attachment of glycans (oligosaccharides) to a nitrogen atom of asparagine (N) residues in the consensus motif Asn-X-Ser/Thr (NXS/T), where X is any amino acid except proline. Therefore, mutations in this posttranslational modification (i.e., N-glycosylation) site cause many human genetic diseases, including cancer. In the past decade, high-throughput quantitative proteome profiling tools have significantly renewed our interest in discovering novel cancer diagnostic or prognostic biomarkers through the simultaneous examination of the enormous amount of high-quality data of thousands of proteins and genes in complex biological systems. In this chapter, we describe how aberrant N-linked glycopeptides could be selectively identified as novel single tumor markers through the use of mass spectrometry (MS)-based proteomics, also known as Solid-phase extraction of N-glycopeptides (SPEG), and reasonable hypotheses that have the potential capacity to revolutionize biomarker discovery and bring those markers to the clinic as early as possible.