The Laboratory of Chemical Glycobiology
Glycobiology is the study of the structures and roles of carbohydrates in biology. Contrary to popular belief, carbohydrates are not simply energy sources but play many essential roles in cell and organismal biology. Various different types of carbohydrate building blocks are known and these can be linked together in various ways by carbohydrate processing enzymes. The resulting carbohydrate structures are attached to other molecules found in cells including proteins and lipids. The carbohydrate structures present within the resulting glycoconjugates continue to be uncovered as important factors in health and disease.
The laboratory of chemical glycobiology headed by Dr. Vocadlo is engaged in the study of; (i) carbohydrate processing enzymes that act on glycoconjugates, (ii) the development of chemical tools to both perturb the action of these enzymes as well as to monitor glycoconjugates, and (iii) theuse of these chemical tools to gain new understanding as to how these enzymes and glycoconjugates mediate cellular and organismal physiology. To realize these aims we study the structures of glycoconjugates using various analytical approaches. We also synthesize substrates to investigate the specificities of carbohydrate processing enzymes and use the methods of physical organic chemistry and biochemistry to understand how such enzymes work to process glycoconjugates. Insights gained through such studies are used to design chemical probes of these enzymes, with a focus on enzyme inhibitors. These probes are validated in vitro, in cells, and in vivo as appropriate. A key objective is to create probes of carbohydrate processing enzymes that can be used to evaluate the roles of interesting glycoconjugates in health and disease. Members of the laboratory come from different backgrounds including, for example, biochemistry, cell biology, and chemistry.
Gloster, T. M. and Vocadlo, D.J. Glycan processing enzyme inhibitors; enabling tools for glycobiology. Nature Chemical Biology. 2012, 8, 683-94.
The O-GlcNAc post-translational modification
One current area of interest is the modification of serine and threonine residues of nuclear and cytoplasmic proteins with N-acetylglucosamine residues in what is known as the O-GlcNAc post-translational modification. This modification is abundant within all multicellular eukaryotes and its levels are maintained by only two enzymes. A glycosyltransferase known as O-GlcNAc transferase (OGT) acts to install O-GlcNAc at sites of modification. A glycoside hydrolase known as O-GlcNAcase (OGA) acts to remove this modification. The coordinated action of these enzymes results in the cycling of O-GlcNAc on proteins. O-GlcNAc has also been shown to be able to influence serine and threonine phosphorylation. O-GlcNAc is therefore a dynamic modification that is able to modulate phosphorylation within signaling pathways. Accordingly, O-GlcNAc has been implicated in various disease states including neurodegeneration.
O-GlcNAc also plays fundamental roles in biology as was recently uncovered in a collaborative effort with the laboratories of Drs. Sinclair, Honda, and Brock, where it was found that OGT is a polycomb group protein, which are protein regulators of gene expression. Owing to the interest in the basic roles of O-GlcNAc we have carried out detailed studies of both OGA and OGT. We continue to explore the catalytic mechanism of OGA and have developed low nanomolar selective inhibitors of this enzyme. We have generated highly selective inhibitors of OGA that cross the blood brain barrier to increase O-GlcNAc levels in the brain and have proposed OGA as a potential therapeutic target for the treatment of Alzheimer disease. Recently we demonstrated in a transgenic tau model, that OGA inhibition decreases tau aggregation and tau-driven neurodegeneration. More recently, we have gained insights into the glycosyltransferase OGT and have developed a Trojan horse strategy to inhibit the OGT in cells with single digit micromolar potency. We are continuing our research in the area, developing and refining chemical probes to determine their generality, as well as using these powerful reagents to study the basic biological roles of O-GlcNAc. We collaborate extensively with researchers world-wide to gain insight into the functions of O-GlcNAc. Among others, we have developed collaborations with structural biologists Dr. Davies at the University of York and Dr. Suzanne Walker at Harvard.
Selected publications (for a complete list see the "publications" link below):
Lazarus, M.B., et al Structural snapshots define the mechanism of O-GlcNAc transferase. Nat. Chem. Biol., 2012, On-line.
Yuzwa, S.A., et al Increasing O-GlcNAc slows neurodegeneration and stabilizes tau against aggregation. Nat. Chem. Biol. 2012, 8, 393-9.
Gloster, T.M., et al. Hijacking a biosynthetic pathway yields a potent glycosyl transferase inhibitor acting in cells. Nat. Chem. Biol. 2011, 7, 174-181.
Sinclair, D.A.R., et al Drosophila O-GlcNAc transferase (OGT) is encoded by the Polycomb group (PcG) gene, super sex combs (sxc). Proc. Natl. Acad. Sci. USA. 2009, 106, 13427-33.