Structural Zn(II) Implies a Switch from Fully Cooperative to Partly Downhill Folding in Highly Homologous Proteins

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• 作者：Maddalena Palmieri ; Gaetano Malgieri ; Luigi Russo ; Ilaria Baglivo ; Sabrina Esposito ; Fortuna Netti ; Annarita Del Gatto ; Ivan de Paola ; Laura Zaccaro ; Paolo V. Pedone ; Carla Isernia ; Danilo Milardi ; Roberto Fattorusso
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：April 3, 2013
• 年：2013
• 卷：135
• 期：13
• 页码：5220-5228
• 全文大小：422K
• 年卷期：v.135,no.13(April 3, 2013)
• ISSN：1520-5126

文摘

In the funneled landscape, proteins fold to their native states through a stochastic process in which the free energy decreases spontaneously and unfolded, transition, native, and possible intermediate states correspond to local minima or saddle points. Atomic description of the folding pathway appears therefore to be essential for a deep comprehension of the folding mechanism. In metallo-proteins, characterization of the folding pathways becomes even more complex, and therefore, despite their fundamental role in critical biological processes, little is known about their folding and assembly. The study of the mechanisms through which a cofactor influences the protein folding/unfolding reaction has been the rationale of the present study aimed at contributing to the search for cofactors鈥?general roles in protein folding reactions. In particular, we have investigated the folding pathway of two homologous proteins, Ros87, which contains a prokaryotic zinc finger domain, and Ml4_52鈥?51, lacking the zinc ion. Using a combination of CD, DSC and NMR techniques, we determined the thermodynamics and the structural features, at an atomic level, of the thermal unfolding of Ros87 and compared them to the behavior of Ml4_52鈥?51. Our results, also corroborated by NMR ¹H/²H exchange measurements, show that the presence of the structural Zn(II) in Ros87 implies a switch from the Ml4_52鈥?51 fully cooperative to a two-step unfolding process in which the intermediate converts to the native state through a downhill barrierless transition. This observation, which has never been reported for any metal ion so far, may have a significant role in the understanding of the protein misfolding associated with the presence of metal ions, as observed in neurodegenerative diseases.