1. Laboratory of Structural BiophysicsBiochemistry and Biophysics CenterNational Heart, Lung, and Blood InstituteNational Institutes of Health Bethesda MD 20892 USA
2. Present address: Ashland Specialty Ingredients 500 Hercules Rd. Wilmington DE 19808 USA
3. Office of Intramural ResearchCenter for Information TechnologyNational Institutes of Health Bethesda MD 20892 USA