Innovative Chemical Tools to Address Analytical Challenges of Protein Phosphorylation and Glycosylation

ConspectusProtein post-translational modifications (PTMs) modulate almost all cellular processes. Aberrant PTMs are closely bound to various human diseases, which greatly complicates the association of a specific disease with a genetic mutation and even renders genomics-driven personalized therapeutics ineffective. PTM proteomics has the potential to provide a more comprehensive understanding of disease biology and is emerging as one of the new breakthroughs of precision medicine in the postgenomics era. As two of the most prominent PTMs, phosphorylation and glycosylation have attracted broad research interest both in academia for the discovery of cancer pathogenesis, biomarkers, and therapeutic targets and in industry for the development of targeted drugs and vaccines. Despite the great rewards, current phosphorylation and glycosylation analyses are still faced with some considerable challenges due to the ultralow abundance of phosphorylation and glycosylation and the grand heterogeneity and structural complexity of glycosylation. To date, our laboratory has concentrated on protein phosphorylation and glycosylation and offered unique insights for the development of innovative separation and analytical tools. An overview of these chemical tools, together with our views on potential solutions to the challenges of protein phosphorylation and glycosylation analysis, is presented in this Account.The first part describes our efforts in phosphorylation enrichment and sensing. Given the excellent responsiveness and expandability of smart polymers, we designed a smart polymer material bearing affinity ligands that target the phosphate group and achieved efficient enrichment of multiply phosphorylated peptides through a tunable catch-and-release. Further, the combination of ligand-bearing smart polymers with solid-state nanochannels for the creation of functional nanofluidic devices is presented. The devices allow us to monitor the kinase reaction, thus providing a low-cost, label-free assay for kinase activity. In the next section, we discuss capture strategies for glycosylated species and glycan analysis methods. A Schiff base-containing material was revealed to achieve high-efficiency capture of sialylated glycopeptides through a hydrolysis reaction, demonstrating the power of dynamic covalent chemistry for enrichment. Then, a directed evolution strategy based on phage display was used to develop a lipopolysaccharide (LPS)-targeted ligand that, when incorporated into a polymer as an adsorbent, can efficiently clear the circulating LPS. Based on the distinction of simple glycan isomers with a nanofluidic device, we further explored the identification of diverse glycans with a protein nanopore through a derivatization strategy. The success of the exploration offers a solution to advance nanopore-based single-molecule glycan profiling and glycan sequencing. Although not comprehensive, this Account could provide new insight into the development of chemical tools to facilitate the analysis of phosphorylation and glycosylation as well as other PTMs.