Funding was provided by the National Institutes of Health (GM122606), the National Science Foundation (CHE1955922), the Kellogg Scripps Graduate Program (Kellogg Fellowship to V.A.V.L.), Nanjing King-Pharm CO, Ltd. (financial support to X. G.) and the Postdoctoral Exchange Fellowship Program by the Office of China Postdoctoral Council (financial support to L. K.).