1. National Glycoengineering Research Center and The State Key Laboratory of Microbial Technology, School of Life Sciences, Shandong University, Shandong 250100, China
2. Departments of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
3. Present address: Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA