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Published June 25, 2002 | Published
Journal Article Open

Using deeply trapped intermediates to map the cytochrome c folding landscape


Replacement of iron with cobalt(III) selectively introduces a deep trap in the folding-energy landscape of the heme protein cytochrome c. Remarkably, neither the protein structure nor the folding thermodynamics is perturbed by this metal-ion substitution, as shown by data from spectroscopic and x-ray diffraction experiments. Through kinetics measurements, we have found parallel folding pathways involving several different misligated Co(III) species, and, as these folding intermediates persist for several hours under certain conditions, we have been able to elucidate fully their spectroscopic properties. The results, along with an analysis of the fluorescence energy-transfer kinetics during refolding, show that rapidly equilibrating populations of compact and extended polypeptide conformations are present until all molecules have reached the native structure. These measurements provide direct evidence that collapsed denatured structures are not substantially more stable than extended conformations of cytochrome c.

Additional Information

© 2002 by the National Academy of Sciences. Contributed by Harry B. Gray, April 30, 2002. This research was supported by the National Science Foundation (MCB 9974477; DBI 9876443) and the Arnold and Mabel Beckman Foundation. Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.rcsb.org (access code 015902) (PDB ID code 1LFM).

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