The unfolding-folding pathways of small iron-sulfur proteins probed by single molecule force spectroscopy
Department of Chemistry, Uiversity of British Columbia, Canada
Abstract: Metal ions play important roles in biology. In metalloproteins, metal centers serve as active sites, as well as important structural elements to facilitate protein folding and assembly. However, it is challenging to investigate the unfolding-folding of metalloproteins due to the loss or decomposition of the metal center. Here, we combine single molecule force spectroscopy (atomic force microscopy and optical tweezers) and protein engineering techniques to investigate the unfolding-refolding mechanism of a small iron sulfur protein rubredoxin and ferredoxin. Our results revealed that the unfolding of both proteins are characterized by the initial partial unfolding of the protein followed by the rupture of the iron sulfur center and complete unraveling of the protein. However, differences in the iron chelation motif in rubredoxin and ferredoxin gave rise to distinct rupture patterns of the iron sulfur center. After complete unfolding, rubredoxin and ferredoxin were observed to refold to its holo-native form with the fully reconstituted iron sulfur center. Moreover, folding of the apo- rubredoxin was observed during the folding of rubredoxin, while apo-ferredoxin was not observed to form, revealing different roles and importance of the iron sulfur center to the holo-proteins. Our results open new avenues towards investigating the folding mechanism of metalloproteins at an unprecedented resolution.
Keywords: single molecule, metalloproteins, force spectroscopy, protein folding
 H. Li and P. Zheng Curr. Opin. Chem. Biol. 2018, 43, 58.
 H. Lei, Y. Guo, X. Hu, C. Hu, X. Hu and H. Li, J. Am. Chem. Soc. 2017, 139, 1358.
 P. Zheng, Y, Wang and H. Li Angew. Chem. Int. Ed. 2014, 53, 14060.
Brief Curriculum Vitae
Hongbin Li obtained his bachelor degree in Polymer Engineering from Tianjin University in 1993 and PhD degree in PolymerChemistry and Physics from Jilin University (with Profs. JIacong Shen, Xi Zhang and Hermann Gaub) in 1998. During his PhD study, he was jointly trained in University of Munich, Germany. After his postdoctoral training in Mayo Medical Center in Rochester, Minnesota, USA (with Prof. Julio Fernandez, 1999-2002), he worked as an Associate Research Scientist in Columbia University, USA. In 2004, he joined the Department of Chemistry in the University of British Columbia, Canada. Currently he is a full Professor in Chemistry. His research interests include protein mechanics and engineering at the single molecule level, protein-based biomaterials, as well as protein folding and unfolding dynamics. He has published more than 130 articles in leading journals, including Nature, Science, PNAS, Nature sister journals, JACS and Angewandte Chemie. His research has been recognized by numerous awards, including the Charles McDowell Award for Excellence in Research, Canada Research Chair in Molecular Nanoscience and Protein Engineering, NSERC Discovery Accelerator Supplement Award, Michael Smith Foundation for Health Research Career Investigator Award, Peter Wall Institute Early Career Award, JILA Distinguished Visitor Fellow and Changjiang Scholar.
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3. Zheng, P., Arantes, G. M., Field, M. J. and Li, H. B. Nature Commun. 2015, 6, 7569.
4. Zheng, P., Wang, Y. and Li, H. Angew. Chem. Int. Ed. 2014, 53, 14060.
5. Kong, N., Peng, Q. and Li, H. Adv. Func. Materi., 2014, 24, 7310.
6. Fang, J., Mehlich, A., Koga, N., Huang, J., Koga, R., Gao, X., Hu, C., Jin, C., Rief, M., Kast, J., Baker, D. and Li, H. Nature Commun., 2013, 4, 2974.
7. Lv, S., Dudek, D.M., Cao, Y., Balamurali, M.M., Gosline, J. and Li, H. Nature, 2010, 465, 69.
8. Cao, Y., Yoo, T. and Li, H. B. Proc. Natl. Acad. Sci. USA 2008, 105, 11152.
9. Cao, Y., and Li, H. B Nature Nanotech. 2008, 3, 512.
10. Fernande, J. and Li, H. Science, 2004, 303, 1674.