1. Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, United States
2. Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011-3260, United States
3. Office of Biotechnology Protein Facility, Iowa State University, Ames, Iowa 50011-3260, United States