Glycomic approaches to study post-translational modification by O-linked beta-N-acetylglucosamine (O-GlcNAc)

The overall goal of my research projects is to understand the complex interplay between post-translational O-GlcNAc and O-Phosphate modifications. Like phosphorylation, O-GlcNAcylation is a one of the major forms of post-translational modification (PTM), and it has been found on numerous nuclear and cytoplasmic proteins that are involved in diverse cellular metabolism and function. Similar to phosphorylation, O-GlcNAcylation occurs on serine or threonine residues of the polypeptide backbones. O-GlcNAcylation is dynamic and has a high cycling rate on many proteins in response to various environmental stimuli. So far, many proteins have been found to be both O-GlcNAcylated and phosphorylated. The "yin-yang" hypothesis states that competition of O-GlcNAc and O-phosphate on the same serine or threonine residue may modulate the function of the protein. However, accumulating evidence has suggested this hypothesis as over-simplified. Global and systematic studies have been proposed and performed using mass spectrometry-based proteomics approaches in order to elucidate the complex interplay between the two abundant post translational modifications. An important aspect of studying post-translational modifications is to map the exact sites of the modifications. Mapping O-GlcNAc sites has been extremely difficult due to their intrinsic lability in the gas phase, low stoichiometry, and signal suppression. To solve this problem, new methods for O-GlcNAc enrichment and site-mapping are developed and optimized.