1. Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
2. Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI 02912, USA.
3. Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, RI 02912, USA.
4. Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756, USA.