Assistant Professor of Biochemistry and Molecular Biology
Ph.D. (1998) Cornell University
Keith.Vosseller@drexelmed.edu

Telephone:  (215) 762-8789

Research Program:
O-GlcNAc is a novel post-translational carbohydrate modification. Unlike classical complex glycosylation, O-GlcNAc is responsive to cell stimuli and modifies a wide variety of cytosolic and nuclear proteins. While O-GlcNAc appears to be a regulatory modification analogous to phosphorylation, specific functions for O-GlcNAc are just starting to be understood. An obstacle to the study of O-GlcNAc has been the inability to identify specific sites of modification on proteins. We’ve recently developed mass spectrometry based techniques to effectively map O-GlcNAc sites on a proteomic scale. We are using proteomics to quantitatively understand post-translational patterns of O-GlcNAc and phosphorylation which regulate systems such as signaling complexes and cellular compartments. There are two main areas of interest.

1. Due to altered metabolic flux of glucose, O-GlcNAc levels are aberrantly increased in type II diabetes. Our work demonstrated that elevated O-GlcNAc in adipocytes contributed to insulin signaling defects associated with diabetic insulin resistance. We and others have identified several key insulin signaling molecules which are modified by O-GlcNAc, such as IRS1, IRS2, and Akt. Insulin signaling appears to operate within compartmentalized signaling domains known as lipid rafts or caveolae. Currently, we are targeting insulin signaling complexes and lipid raft domains to quantitatively identify site-specific O-GlcNAc and phosphorylation events in the context of insulin stimulation and insulin resistance. This will help us develop models of post-translational control in this critical signaling system. More importantly, O-GlcNAc sites identified will be tested for specific regulatory functions in insulin signaling.

2. Accumulating evidence suggests an important role for O-GlcNAc in the brain. The enzymes catalyzing addition (OGT) and removal (O-GlcNAcase) of O-GlcNAc are most abundant in brain, and brain specific knock-out of OGT indicates a critical role for O-GlcNAc in neuronal development and synaptic processes. In a recent proteomic study, we discovered a striking enrichment of O-GlcNAc at both presynaptic and postsynaptic terminals. Site-specific O-GlcNAc analysis revealed modification of proteins critical to excitatory Glutamate receptor signaling, such as Shank2 and Synaptic RasGap. Additionally, members of a class of presynaptic proteins (e.g. Bassoon and Piccolo), which localize to “active zones” where they function in synaptic vesicle docking and release, were found to be extensively modified by O-GlcNAc. We are continuing to use proteomics to quantitatively identify O-GlcNAc and phosphorylation events important in synaptic transmission towards a goal of understanding site-specific regulatory influences of O-GlcNAc in this system.    

Selected Publications

1. Vosseller, K.; Trinidad, J. C.; Chalkley, R. J.; Specht, C. G.; Thalhammer, A.; Lynn, A. J.; Snedecor, J. H.; Guan, S.; Medzihradszky, K. F.; Maltby, D. A.; Schoepfer, R.; Burlingame, A. L., O-GlcNAc proteomics of postsynaptic density preparations using lectin weak affinity chromatography (LWAC) and mass spectrometry. Mol Cell Proteomics 2006.

2. Vosseller, K.; Hansen, K. C.; Chalkley, R. J.; Trinidad, J. C.; Wells, L.; Hart, G. W.; Burlingame, A. L., Quantitative analysis of both protein expression and serine / threonine post-translational modifications through stable isotope labeling with dithiothreitol. Proteomics 2005, 5, (2), 388-98.

3. Slawson, C.; Zachara, N. E.; Vosseller, K.; Cheung, W. D.; Lane, M. D.; Hart, G. W., Perturbations in O-linked beta-N-acetylglucosamine protein modification cause severe defects in mitotic progression and cytokinesis. J Biol Chem 2005, 280, (38), 32944-56.

4. Wells, L.; Vosseller, K.; Hart, G. W., A role for N-acetylglucosamine as a nutrient sensor and mediator of insulin resistance. Cell Mol Life Sci 2003, 60, (2), 222-8.

5. Wells, L.; Vosseller, K.; Cole, R. N.; Cronshaw, J. M.; Matunis, M. J.; Hart, G. W., Mapping sites of O-GlcNAc modification using affinity tags for serine and threonine post-translational modifications. Mol Cell Proteomics 2002, 1, (10), 791-804.

6. Vosseller, K.; Wells, L.; Lane, M. D.; Hart, G. W., Elevated nucleocytoplasmic glycosylation by O-GlcNAc results in insulin resistance associated with defects in Akt activation in 3T3-L1 adipocytes. Proc Natl Acad Sci U S A 2002, 99, (8), 5313-8.

7. Wells, L.; Gao, Y.; Mahoney, J. A.; Vosseller, K.; Chen, C.; Rosen, A.; Hart, G. W., Dynamic O-glycosylation of nuclear and cytosolic proteins: further characterization of the nucleocytoplasmic beta-N-acetylglucosaminidase, O-GlcNAcase. J Biol Chem 2002, 277, (3), 1755-61.

8. Vosseller, K.; Sakabe, K.; Wells, L.; Hart, G. W., Diverse regulation of protein function by O-GlcNAc: a nuclear and cytoplasmic carbohydrate post-translational modification. Curr Opin Chem Biol 2002, 6, (6), 851-7.

9. Vosseller, K.; Wells, L.; Hart, G. W., Nucleocytoplasmic O-glycosylation: O-GlcNAc and functional proteomics. Biochimie 2001, 83, (7), 575-81.

10. Wells, L.; Vosseller, K.; Hart, G. W., Glycosylation of nucleocytoplasmic proteins: signal transduction and O-GlcNAc. Science 2001, 291, (5512), 2376-8.

11. Comer, F. I.; Vosseller, K.; Wells, L.; Accavitti, M. A.; Hart, G. W., Characterization of a mouse monoclonal antibody specific for O-linked N-acetylglucosamine. Anal Biochem 2001, 293, (2), 169-77.