1. Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
2. Institute for Protein Design, University of Washington, Seattle, WA 98195, USA.
3. Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/3, 8010-Graz, Austria.
4. Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK.
5. Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA.
6. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
7. Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA.