Seeing the forest through the trees: characterizing the glycoproteome

Post-translational modifications (PTMs) immensely expand the diversity of the proteome. Glycosylation, among the most ubiquitous PTMs, is a dynamic and multifarious modification of proteins and lipids that generates an omnipresent foliage on the cell surface. The resulting protein glycoconjugates can serve important functions in biology. However, their vast complexity complicates the study of their structures, interactions, and functions. There is now a growing appreciation of the need to study glycans and proteins together as complete entities, as the sum of these two components can exhibit unique functions. In this review, we discuss the growing forestry toolbox to characterize the structure, interactions, and biological functions of protein glycoconjugates, as well as the potential payouts of understanding and controlling these enigmatic biomolecules. Glycosylation is an omnipresent post-translational modification that expands the functional diversity of the proteome.This resulting glycoproteome is a heterogeneous and dynamic forest that forms cis and trans interactions with other biomolecules and small molecule therapeutics.There is an emerging realization that glycoconjugates are more than the sum of their individual glycan and protein components and that understanding their biology at the conjugate level can pay enormous dividends in biomarker and drug discovery.The fast-expanding glyco-toolkit is moving towards bridging the glycome and proteome at every level, from glycan arrays to glycoproteomics to cryoelectron microscopy.These ongoing characterization and analytical efforts are enabled by parallel and synergistic innovations in defining and understanding glycoproteome heterogeneity and interactions.