[1] Nankai Univ, Sch Math Sci, Tianjin, Peoples R China
[2] Shandong Univ, Res Ctr Math & Interdisciplinary Sci, Qingdao, Shandong, Peoples R China
[3] Univ Washington, Dept Biochem, Seattle, WA USA
[4] Univ Washington, Inst Prot Design, Seattle, WA USA
[5] Univ Washington, Howard Hughes Med Inst, Seattle, WA USA