1. Center for Neurologic Diseases, Brigham and Women's Hospital and Department of Neurology, Harvard Medical School, 65 Landsdowne Street, Cambridge, Massachusetts 02139, Department of Biochemistry and Program in Structural Biology, Weill Medical College of Cornell University, New York, New York 10021, and Laboratory of Molecular Neurobiology and Neuroproteomics, Brain Mind Institute, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland