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The protein-folding speed limit: Intrachain diffusion times set by electron-transfer rates in denatured Ru(NH3)(5)(His-33)-Zn-cytochrome c

Chang, I-Jy and Lee, Jennifer C. and Winkler, Jay R. and Gray, Harry B. (2003) The protein-folding speed limit: Intrachain diffusion times set by electron-transfer rates in denatured Ru(NH3)(5)(His-33)-Zn-cytochrome c. Proceedings of the National Academy of Sciences of the United States of America, 100 (7). pp. 3838-3840. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:CHApnas03

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Abstract

The kinetics of electron transfer from the triplet-excited Zn-porphyrin to a Ru(NH3)(5)(His-33)(3+) complex have been measured in Zn-substituted ruthenium-modified cytochrome c under denaturing conditions. In the folded protein, the electron-tunneling rate constant is 7.5 x 10(5) s(-1). As the protein is denatured with guanidine hydrochloride, a faster adiabatic electron-transfer reaction appears (4.0 x 10(6) s(-1), [guanidine hydrochloride] = 5.4 M) that is limited by the rate of intrachain diffusion to bring the Zn-porphyrin and Ru complex into contact. The 250-ns contact time for formation of a 15-residue loop in denatured cytochrome c is in accord with a statistical model developed by Camacho and Thirumalai [Camacho, C. J. & Thirumalai, D. (1995) Proc. Natl. Acad. Sci. USA 92, 1277-1281] that predicts that the most probable transient loops formed in denatured proteins are comprised of 10 amino acids. Extrapolation of the cytochrome c contact time to a 10-residue loop sets the folding speed limit at approximate to10(7) s(-1).


Item Type:Article
Additional Information:© 2003 by the National Academy of Sciences. Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved January 30, 2003 (received for review November 29, 2002). Published online before print March 19, 2003. I-J.C. gratefully acknowledges financial support from the National Taiwan Normal University and the National Science Council of the Republic of China. J.C.L. thanks the Ralph M. Parsons Foundation for a graduate fellowship. This work was supported by National Science Foundation Grant MCB 9974477 and the Arnold and Mabel Beckman Foundation.
Subject Keywords:INTRAMOLECULAR CONTACT FORMATION, UNFOLDED CYTOCHROME-C, TRANSFER KINETICS, DEPENDENCE, DYNAMICS
Record Number:CaltechAUTHORS:CHApnas03
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:CHApnas03
Alternative URL:http://dx.doi.org/10.1073/pnas.0637283100
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:626
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:08 Sep 2005
Last Modified:14 Nov 2014 19:18

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