Glycomics and glycoproteomics of membrane proteins and cell-surface receptors: Present trends and future opportunities

Abstract

Membrane proteins mediate cell-cell interactions and adhesion, the transfer of ions and metabolites, and the transmission of signals from the extracellular environment to the cell interior. The extracellular domains of most cell membrane proteins are glycosylated, often at multiple sites. There is a growing awareness that glycosylation impacts the structure, interaction, and function of membrane proteins. The application of glycoproteomics and glycomics methods to membrane proteins has great potential. However, challenges also arise from the unique physical properties of membrane proteins. Successful analytical workflows must be developed and disseminated to advance functional glycoproteomics and glycomics studies of membrane proteins. This review explores the opportunities and challenges related to glycomic and glycoproteomic analysis of membrane proteins, including discussion of sample preparation, enrichment, and MS/MS analyses, with a focus on recent successful workflows for analysis of N- and O-linked glycosylation of mammalian membrane proteins.

Keywords: Glycomics; Glycopeptides; Glycoproteomics; Membrane proteins; Receptors.

Figure 1

Schema of Glycomics and Glycoproteomics Workflow for Membrane Proteins.

Figure 2. The Impact of N-Glycosylation on Epidermal Growth Factor Receptor (EGFR) Dimerization, Activation, and Signaling

A. The extracellular (E) domain of EGFR (dark gray box) is N-glycosylated at multiple sites, whereas the transmembrane region (gray wavy line) and cytosolic (C) (light gray box) domains are not glycosylated. B. Increased sialylation of glycans on the receptor suppresses ligand-induced dimerization and activation. C. Increases in the number of alpha 1,3-fucosylated N-glycans also suppress ligand-induced dimerization and activation. Dark squares: N-acetylglucosamine; gray circles: mannose; light circles: galactose; diamonds: sialic acid. ‘E’ indicates extracellular, ‘C’ indicates cytoplasmic. Circled ‘P’ indicates phosphorylation. Circled ‘EGF’ represents the ligand. Sources: Fernandes et al., 2001 [4], Liu et al., 2011 [6], Yen et al., 2015 [7], Kaszuba et al., 2015 [5].