1. School of Medicine, Stanford University, Stanford, CA 94305, USA.
2. Institute of Bioorganic Chemistry, Russian Academy of Science, 117871 Moscow, Russia.
3. Center for Molecular Modeling, Center for Information Technology, NIH, Building 12A, Bethesda, MD 20892, USA.
4. Clontech Laboratories, 1020 East Meadow Circle, Palo Alto, CA 94303, USA.