Recognition and Deconstruction of Uronic Acid-Containing Polysaccharides

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Beyond the universally recognized role for carbohydrates as nutrient sources, complex carbohydrates in the form of polysaccharides, proteoglycans, and glycolipids may be considered to be the "the language of the cell" in that they mediate many integral biological events. In an effort to decipher the role that a class of carbohydrates, the uronic-acid containing polysaccharides (UCPs), play in these processes, I will pursue the structural and functional characterization of the proteins involved in carbohydrate recognition and metabolism. UCPs are compositionally similar in that they are made up of repeating elements that include either beta-D-glucuronic acid, alpha-D-galacturonic acid, alpha-D-4-O-methylglucuronic acid, or their derivatives along the chain lengths. However, despite this compositional similarity, UCPs mediate many diverse biological interactions and cell-signaling events. For example: UCPs contribute unique mechanical, viscoelastic, and osmotic potential at cell and tissue surfaces they participate in ligand, nutrient, and cellular motility throughout the extracellular matrix, and they interact with a variety of effector molecules to mediate intracellular interactions. While the long-term objective of my research will address UCPs in general, the initial focus will be on two carbohydrates in particular, hyaluronan and pectin (homogalacturonate). This research focus is based on the hypothesis: that structural and functional reconstruction of microbial systems for UCP metabolism will bridge the knowledge gap between subtle differences in UCP composition and their diverse biological functions. **Despite their biological significance and industrial relevance as non-toxic composites, hyaluronan and pectin metabolism is a largely underexplored branch of glycobiology. For example, a novel class of pectin-degrading enzymes has been reported within the past three years and my own work has identified the first microbial hyaluronan binding protein. I have therefore applied a discovery-based bioinformatics approach to identify a series of novel hyaluronan and pectin-related genes that will be the focus of our proposed research program. The long-term objective of the program is to study hyaluronan and pectin recognition and metabolizing protein factors by 3-D structure determination, and to use supportive kinetic and thermodynamic techniques to probe molecular interactions and mechanisms of action. Specifically, my trainees and I will use X-ray crystallography and Small Angle X-ray Scattering for structural characterization and various complementary molecular characterization techniques, including bioinformatics, glycobiology, enzymology, calorimetry and protein biochemistry, to correlate structure and function. This unified approach to molecular characterization and functional analyses will allow us to address important biological processes from multiple perspectives and enhances the impact of the overarching objective of our research program, which is to enrich our understanding of hyaluronan and pectin metabolism; two prominent polysaccharides that make considerable contributions to the coordination of biological events in the extracellular matrix and plant cell walls, respectively.