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Early events in the folding of four-helix-bundle heme proteins

Faraone-Mennella, Jasmin and Gray, Harry B. and Winkler, Jay R. (2005) Early events in the folding of four-helix-bundle heme proteins. Proceedings of the National Academy of Sciences of the United States of America, 102 (18). pp. 6315-6319. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:FARpnas05

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Abstract

Topologically homologous four-helix-bundle heme proteins exhibit striking diversity in their refolding kinetics. Cytochrome b(562) has been reported to fold on a submillisecond time scale, whereas cytochrome c' refolding requires 10 s or more to complete. Heme dissociation in cytochrome b(562) interferes with studies of folding kinetics, so a variant of cytochrome b(562) (cytochrome c-b(562)) with a covalent c-type linkage to the heme has been expressed in Escherichia coli. Early events in the electron transfer-triggered folding of Fe-II-cytochrome c-b(562), along with those of Fe-II-cytochrome c(556), have been examined by using time-resolved absorption spectroscopy. Coordination of S(Met) to Fe-II occurs within 10 mu(s) after reduction of the denatured Fe-III-cytochromes, and shortly thereafter (100 mu(s)) the heme spectra are indistinguishable from those of the folded proteins. Under denaturing conditions, carbon monoxide binds to the Fe-II-hemes in approximate to 15 ms. By contrast, CO binding cannot compete with refolding in the Fe-II-cytochromes, thereby confirming that the polypeptide encapsulates the heme in <10 ms. We suggest that Fe-S(Met) ligation facilitates refolding in these four-helix-bundle heme proteins by reducing the conformational freedom of the polypeptide chain.


Item Type:Article
Additional Information:Copyright © 2005 by the National Academy of Sciences. Contributed by Harry B. Gray, March 21, 2005. This research was supported by National Institutes of Health Grant GM068461, Department of Energy Grant DE-FG02-02ER15359, and the Arnold and Mabel Beckman Foundation.
Subject Keywords:cytochrome, electron transfer, protein folding, unfolded polypeptide-chains, Escherichia-coli, cytochrome B(562), rhodopseudomonas-palustris, speed limit, energy-transfer, kinetics, dynamics, model
Record Number:CaltechAUTHORS:FARpnas05
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:FARpnas05
Alternative URL:http://dx.doi.org/10.1073/pnas.0502301102
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:990
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Nov 2005
Last Modified:14 Nov 2014 19:18

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