期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2005
卷号：102
期号：18
页码：6315-6319
DOI：10.1073/pnas.0502301102
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Topologically homologous four-helix-bundle heme proteins exhibit striking diversity in their refolding kinetics. Cytochrome b562 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 b562 interferes with studies of folding kinetics, so a variant of cytochrome b562 (cytochrome c-b562) with a covalent c-type linkage to the heme has been expressed in Escherichia coli. Early events in the electron transfer-triggered folding of FeII-cytochrome c-b562, along with those of FeII-cytochrome c556, have been examined by using time-resolved absorption spectroscopy. Coordination of S(Met) to FeII occurs within 10 {micro}s after reduction of the denatured FeIII-cytochromes, and shortly thereafter (100 {micro}s) the heme spectra are indistinguishable from those of the folded proteins. Under denaturing conditions, carbon monoxide binds to the FeII-hemes in {approx}15 ms. By contrast, CO binding cannot compete with refolding in the FeII-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.
关键词：cytochrome ; electron transfer ; protein folding
