Organic Chemistry Seminar

Wednesday, September 19th
Professor Xi Chen
"Chemoenzymatic Approaches to Studying Carbohydrate-Binding Proteins"

4:15pm - 5:15pm
Braun Lecture Hall
S.G.Mudd Chemistry Building
Stanford University

This seminar is free and open to the public. All Stanford University Chemistry students are encouraged to attend this special event.




About the Seminar:
The important roles of carbohydrates have been increasingly recognized. Among common carbohydrates, sialic acid-containing structures have attracted much attention. Compared to monosaccharides of five- or six- carbons, sialic acids containing a 9-carbon backbone are much more complex. Structural modifications on sialic acid residues further increase the complexity of sialic acid-containing structures. Currently, more than 50 sialic acid structures have been found in nature. These include three basic forms: N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc), deaminoneuraminc acid (KDN), and their modified forms with substitutions, such as 8-O-methylation, 8-O-sulfation, 9-O-lactylation, 9-O-phosphorylation and single or multiple O-acetylation at C-4, C-5, C-7, C-8, and/or C-9 positions.1 Most of these naturally existing modifications are post-glycosylational modifications.2

Sialic acids have been predominantly found as the terminal carbohydrate units on glycoproteins and glycolipids of vertebrates or as components of capsular polysaccharides and lipooligosaccharides of pathogenic bacteria. As the frontline encountered by other molecules, sialic acids play pivotal roles in many physiologically and pathologically important processes, including cellular recognition and communication, bacterial and viral infection, and tumor metastasis, etc.[1] In order to understand the structure-function relationship of sialic acid modifications, my laboratory has established and developed highly efficient chemoenzymatic methods to obtain structurally defined homogenous sialic acid-containing structures with naturally occurring sialic acid modifications which are difficult to be obtained either by isolation or by chemical synthesis. Their non-natural derivatives can also be obtained similarly.3 These compounds have been used as invaluable probes for studying the important biological roles of sialosides and sialic acid-recognizing proteins.4

1. (a) Angata, T.; Varki, A. Chem. Rev. 2002, 102, 439. (b) Schauer, R. Glycoconj. J. 2000, 17, 48. 2. Yu, H.; Chen, X. Org. Biomol. Chem. 2007, 5, 865. 3. (a) Yu, H.; Yu, H.; Karpel, R.; Chen, X. Bioorg. Med. Chem. 2004, 12, 6427; (b) Yu, H.; Chokhawala, H.; Karpel, R.; Yu, H.; Wu, B.; Zhang, J.; Zhang, Y.; Jia, Q.; Chen, X. J. Am. Chem. Soc. 2005, 127, 17618; (c) Yu, H.; Huang, S.; Chokhawala, H.; Sun, M.; Zheng, H.; Chen, X. Angew. Chem. Int. Ed., 2006, 45, 3938; (d) Yu, H.; Chen X. Org. Lett. 2006, 8, 2393; (e) Yu, H.; Chokhawala, H.; Huang, S.; Chen X. Nature Protocols. 2006, 1, 2485; (f) Huang, S.; Yu, H.; Chen, X. Angew. Chem. Int. Ed. 2007, 5, 2249; (g) Yu, H.; Chokhawala, H. A.; Varki, A.; Chen, X. Org. Biomol. Chem. 2007, 5, 2458; (h) Chokhawala, H. A.; Cao, H.; Yu, H.; Chen, X. J. Am Chem. Soc. 2007, 129, 10630; (i) Muthana, S.; Yu, H.; Huang, S.; Chen, X. J. Am. Chem. Soc. In press. 4. (a) Chokhawala, H.; Yu, H.; Chen X. ChemBioChem 2007, 8, 194; (b) Ni, L.; Chokhawala, H. A.; Cao, H.; Hening, R.; Ng, L.; Huang, S.; Yu, H.; Chen, X.; Fisher, A. J. Biochemistry, 2007, 46, 6288.

About Chen:
Prof. Xi Chen received her B.S. in Chemistry from Xiamen University in 1994 and her Ph.D. in Biological/Organic Chemistry from Wayne State University in 2000. She worked at Neose Technologies, Inc. for two and a half years before joined the faculty in the Department of Chemistry at the University of California, Davis in August 2003. Currently, the research interests of her laboratory are: 1) developing chemoenzymatic approaches for synthesizing structurally defined complex carbohydrate-containing structures; 2) studying carbohydrate-protein interactions; 3) collaborative crystal structure studies, enzyme mechanistic studies, and mutagenesis of glycosyltransferases and other carbohydrate biosynthetic enzymes. Prof. Chen has received an NSF CAREER Award and a Beckman Young Investigator Award.

Questions
Please contact Patricia Dwyer at 650-723-4770.