1. Institute for Protein Design, University of Washington, 3946 W Stevens Way NE, Seattle, Washington 98195, United States
2. Department of Biochemistry, University of Washington, Seattle, Washington 98195, United States
3. Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, United States
4. Manchester Institute of Biotechnology, School of Chemistry, 131 Princess Street, The University of Manchester, Manchester M1 7DN, U.K.