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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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.
|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|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||22 Nov 2005|
|Last Modified:||26 Dec 2012 08:42|
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