from S. Roseman, JBC (2001)

Importance of complex glycans in cell biology

The central dogma of molecular biology has been that biological information moves from DNA to RNA to protein. However, there is a growing appreciation that posttranslational modifications, such as protein glycosylation, dramatically increase polypeptide complexity and function. Glycans are chains of monosaccharides that are covalently linked to cell surface proteins and lipids. They have been recognized as key participants in cell-cell communications and for instance, in the brain, are crucial mediators in neurite outgrowth, synapse formation and plasticity. From a pathological point of view, changes in the neuro-glycome of cells are associated with developmental disorders, can mark the onset of glioma and neuro-inflammation. Despite these intriguing observations, the molecular mechanisms by which these complex carbohydrates influence neural cells are not well understood due to their inherent structural complexity and a lack of suitable biochemical methods to study them. To address these limitations, our research group focusses on two major lines of research.

Fluorogenic biooorthogonal tagging for the visualization of glycans with high signal to background ratio

Although protein tracking in living cells has become routine experiments in cell biology laboratories thanks to the utilization of genetic reporters, glycans are, unfortunately, not amenable to these imaging techniques. As an emerging alternative, the bioorthogonal chemical reporter strategy, which elegantly combines the use of metabolically labeled unnatural sugars (metabolic oligosaccharide engineering) and highly reactive cyclooctyne probes, is a versatile technology for labeling and visualizing glycans. However, cyclooctyne probes are often highly hydrophobic, which can promote their sequestration by membranes, thereby increasing background signal.

To address these difficulties, we are developing fluorogenic biooorthogonal systems (in which non- or weakly fluorescent reagents produce highly fluorescent products) that offer the unique opportunity to label biomolecules without the need for probe washout, a key benefit for intracellular labeling in living systems. The study of these systems are interdisciplinary by nature, involving molecular design and organic chemistry for the probes preparation, photophysics for the characterization of the fluorescence properties and biochemistry / cell imaging for testing the probe in biological systems.

Probing the biosynthesis of complex glycans

Our lab is developing novel unnatural sugars (modified with chemical reporters) that gives us the ability to track carbohydrates in living cells, which in turn can provide us with valuable insights into the biosynthesis and trafficking of glycans. For this purpose, we employed a multidisciplinary approach, including chemo-enzymatic synthesis for the generation of the unnatural sugars, in vitro enzymatic assays for probing the glyco-biosynthetic pathways and cell imaging for visualizing glycans in living cells.