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Early Events, Kinetic Intermediates and the Mechanism of Protein Folding in Cytochrome c
Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95046, USA
* Author to whom correspondence should be addressed.
Received: 26 February 2009; in revised form: 27 March 2009 / Accepted: 30 March 2009 / Published: 1 April 2009
Abstract: Kinetic studies of the early events in cytochrome c folding are reviewed with a focus on the evidence for folding intermediates on the submillisecond timescale. Evidence from time-resolved absorption, circular dichroism, magnetic circular dichroism, fluorescence energy and electron transfer, small-angle X-ray scattering and amide hydrogen exchange studies on the t £ 1 ms timescale reveals a picture of cytochrome c folding that starts with the ~ 1-ms conformational diffusion dynamics of the unfolded chains. A fractional population of the unfolded chains collapses on the 1 – 100 ms timescale to a compact intermediate IC containing some native-like secondary structure. Although the existence and nature of IC as a discrete folding intermediate remains controversial, there is extensive high time-resolution kinetic evidence for the rapid formation of IC as a true intermediate, i.e., a metastable state separated from the unfolded state by a discrete free energy barrier. Final folding to the native state takes place on millisecond and longer timescales, depending on the presence of kinetic traps such as heme misligation and proline mis-isomerization. The high folding rates observed in equilibrium molten globule models suggest that IC may be a productive folding intermediate. Whether it is an obligatory step on the pathway to the high free energy barrier associated with millisecond timescale folding to the native state, however, remains to be determined.
Keywords: Collapsed intermediate; secondary structure formation; disordered tertiary structure; conformational diffusion; unfolded chains; molten globule; heme misligation; time-resolved spectroscopy; far-UV circular dichroism; magnetic circular dichroism; Trp59 fluorescence; amide hydrogen exchange; small-angle X-ray scattering; thermophiles; three-state pathway
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MDPI and ACS Style
Goldbeck, R.A.; Chen, E.; Kliger, D.S. Early Events, Kinetic Intermediates and the Mechanism of Protein Folding in Cytochrome c. Int. J. Mol. Sci. 2009, 10, 1476-1499.
Goldbeck RA, Chen E, Kliger DS. Early Events, Kinetic Intermediates and the Mechanism of Protein Folding in Cytochrome c. International Journal of Molecular Sciences. 2009; 10(4):1476-1499.
Goldbeck, Robert A.; Chen, Eefei; Kliger, David S. 2009. "Early Events, Kinetic Intermediates and the Mechanism of Protein Folding in Cytochrome c." Int. J. Mol. Sci. 10, no. 4: 1476-1499.