1. Center for Epigenetics, Van Andel Research Institute, 333 Bostwick Avenue, NE, Grand Rapids, Michigan 49503, USA
2. Laboratory of Structural Sciences, Van Andel Research Institute, 333 Bostwick Avenue, NE, Grand Rapids, Michigan 49503, USA
3. VARI/SIMM Center, CAS-Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China