1. Key Laboratory for Molecular Enzymology and Engineering of the Ministry of Education; Jilin University; 2699 QianJin Street Changchun 130012 China
2. National Engineering Laboratory for AIDS Vaccine; Jilin University; 2699 QianJin Street Changchun 130012 China
3. School of Life Sciences; Jilin University; 2699 QianJin Street Changchun 130012 China
4. Department of Biochemistry and Molecular Genetics; University of Colorado School of Medicine, Structural Biology and Biochemistry; 12801 E. 17th Avenue, MS 8101 Aurora CO 80045 USA