1. McGovern Institute for Brain Research at MIT Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3. National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
4. Genetic Information Research Institute, 20380 Town Center Ln, Suite 240, Cupertino, CA, USA.
5. Structural Biology Division, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo 153-8904, Japan.
6. Department of Molecular and Mechanistic Immunology, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8510, Japan.