1. US DOE Ames Laboratory Division of Materials Science and Engineering Ames IA 50011 USA
2. Department of Chemical and Biological Engineering Iowa State University Ames IA 50011 USA
3. Roy J. Carver Department of Biochemistry Biophysics and Molecular Biology Iowa State University Ames IA 50011 USA
4. Department of Structural Biology University of Pittsburgh Pittsburgh PA 15261 USA