1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, U.S.A.
2. Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, U.S.A.
3. Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
4. Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, U.S.A.
5. BIOSS Centre for Biological Signaling Studies, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany.
6. Department of Chemistry, University of California, Irvine, CA 92697, U.S.A.