1. Biosciences DivisionArgonne National LaboratoryArgonne Illinois60439
2. Institut Laue‐LangevinCS 20156, 38042 Grenoble Cedex 9 France
3. Department of Biological SciencesCarnegie Mellon UniversityPittsburgh Pennsylvania15213
4. Department of BioengineeringNortheastern UniversityBoston Massachusetts02115