Glycomic Approaches to Study GlcNAcylation: Protein Identification, Site-mapping, and Site-specific O-GlcNAc Quantitation

Background O -Linked β - N -acetylglucosamine ( O -GlcNAc) is an enzyme-catalyzed posttranslational modification of serine or threonine side chains of nuclear and cytoplasmic proteins. O -GlcNAc is present in all metazoans and in viruses that infect eukaryotic cells. GlcNAcylation is dynamic and has a high cycling rate on many proteins in response to cellular metabolism and various environmental stimuli. The rapid cycling of O -GlcNAc modulates many biological processes, including transcriptional regulation, stress responses, cell cycle regulation, and protein synthesis and turnover. Rationale Despite the importance of O -GlcNAc, progress during the past two decades in this field has been slow. One of the major obstacles is the lack of simple and sensitive tools for efficient O -GlcNAc detection and localization. Recently developed O -GlcNAc derivatization and enrichment approaches, together with new techniques in mass spectrometric instrumentation and methods, have provided breakthroughs in O -GlcNAc site localization and site-specific quantitation. In this review, we will discuss how the current techniques are expanding our knowledge about O -GlcNAc proteomics/glycomics and functions.