1. Center for Biomolecular Structure and Organization, Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
2. Department of Biochemistry, University of Colorado, Boulder, CO 80309, USA
3. Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, CA 93106, USA
4. Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106, USA