1. Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602, USA.
2. Chemistry Department, University of Georgia, Athens, GA 30602, USA.
3. Departments of Cell and Molecular Biology, and Chemical Physiology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.