Cell surface glycoproteomics: deciphering glycoproteins through a unique analytical capture approach

Cell surface proteins (CSPs) are often involved in various biological processes such as cell-cell interactions, immune responses, and molecular transport. The abnormal expression of CSP usually indicates the occurrence and development of human diseases. Most CSPs are glycosylated and have been explored as potential drug targets and disease biomarkers; however, efficient isolation of CSPs from intracellular proteins is difficult due to their low abundance and strong hydrophobicity. The comprehensive characterization of surface glycoproteins remains a great challenge and is often underrepresented in proteomics. In recent years, unprecedented progress has been made in the mass spectrometry analysis of surface proteins, and CSP capture methods and mass spectrometry have been greatly developed. In this article, we aim to give a comprehensive overview of innovative analytical methods that can enrich CSPs, including centrifugation-based separation, phase partitioning, adhesion-based capture of surface proteins, antibody or lectin affinity, and biotin-based chemical labeling. Surface glycoproteins are captured by chemical oxidation of glycans or click chemistry for carbohydrate metabolic labeling. These techniques offer a wide range of applications for studying the function of cell surface receptors and identifying markers for diagnostic and therapeutic development.