1. Biophysics Laboratory, Center for Biologics Evaluation & Research, Food & Drug Administration, Rockville, Maryland 20852-1448
2. Department of Chemical Engineering, University of WisconsinMadison, Madison Wisconsin 53706
3. Department of Gastroenterology, Walter Reed Army Institute of Research, Washington, DC 20307
4. Laboratory of Structural Biology, Division of Computer Research & Technology, National Institutes of Health, Bethesda, Maryland 20892