1. Complex Carbohydrate Research Center University of Georgia Athens GA 30602 USA
2. Department of Ophthalmology and Visual Sciences University of Illinois at Chicago Chicago IL 60612 USA
3. Department of Chemical Biology and Drug Discovery Utrecht Institute for Pharmaceutical Sciences Utrecht University 3584 CG Utrecht The Netherlands
4. Current address: CICbioGUNE Basque Research & Technology Alliance (BRTA) Bizkaia Technology Park 48160 Derio, Bizkaia Spain
5. Bijvoet Center for Biomolecular Research Utrecht University 3584 CG Utrecht The Netherlands
6. Department of Chemistry University of Georgia Athens GA 30602 USA