1. Department of Integrative Structural and Computational Biology The Scripps Research Institute 10550 N. Torrey Pines Road, MB 44 La Jolla CA 92037 USA
2. Present address: Genentech, Inc. 1 DNA Way South San Francisco CA 94080 USA
3. Department of Chemistry and Biochemistry University of California, San Diego La Jolla CA 92093 USA
4. National Biomedical Computation Resource University of California, San Diego La Jolla CA 92093 USA
5. 5820 Nancy Ridge Drive San Diego CA 92121 USA
6. Institute for Molecular Biology and Biophysics ETH Zürich Zürich Switzerland