1. Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
2. Department of Structural Biology, Genentech, South San Francisco, CA 94080, USA.
3. Department of Research Biology, Genentech, South San Francisco, CA 94080, USA.
4. Department of Biochemical and Cellular Pharmacology, Genentech, South San Francisco, CA 94080, USA.
5. Departments of Chemistry/Biochemistry and Pharmacology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
6. Department of Pathology, Genentech, South San Francisco, CA 94080, USA.
7. Department of Physiological Chemistry, Genentech, South San Francisco, CA 94080, USA.