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Published January 2, 2007 | Published
Journal Article Open

Site-specific collapse dynamics guide the formation of the cytochrome c' four-helix bundle

Abstract

The evolution of tryptophan-to-heme (W/heme) distance distributions extracted from analysis of fluorescence energy transfer kinetics during the refolding of Rhodopseudomonas palustris cytochrome c' reveals dramatic differences between two variants [W32 (Q1A/F32W/W72F) and W72 (Q1A)]. Both W32/heme and W72/heme distance distributions measured at the earliest time point attainable with a continuous-flow mixer (150 µs) confirm that the polypeptide ensemble is not uniformly collapsed and that native structure is not formed. Time-resolved fluorescence spectra indicate that W32 is sequestered from the aqueous solution during the first 700 µs of folding, whereas W72 remains exposed to solvent. The first moment of the W32/heme distance distribution evolves to its native value faster than that of W72, suggesting that the approach of W32 to the heme precedes that of W72.

Additional Information

© 2006 The National Academy of Sciences of the USA. Contributed by Harry B. Gray, October 24, 2006 (received for review October 12, 2006). Published online before print December 19, 2006, 10.1073/pnas.0609413103 We thank Dr. Linda Thöny-Meyer (Eidgenössiche Technische Hochschule, Zürich, Switzerland) for the ccm plasmid pEC86 and Ekaterina V. Pletneva for numerous discussions. This work was supported by National Institutes of Health Grant GM068461 (to J.R.W.), the Arnold and Mabel Beckman Foundation (Beckman Senior Research Fellowship to J.C.L.), and the Ellison Medical Foundation (Senior Scholar Award in Aging to H.B.G.). T.K. was supported by a Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists. Author contributions: T.K. and J.R.W. designed research; T.K. and J.C.L. performed research; T.K. and J.C.L. analyzed data; and T.K., J.C.L., H.B.G., and J.R.W. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0609413103/DC1.

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