Ligand exchange during cytochrome c folding

Syun Ru Yeh, Satoshi Takahashi, Baochen Fan, Denis L. Rousseau

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134 Scopus citations


Submillisecond folding of cytochrome c reveals that a nascent phase appears within the mixing dead time of 100 μs, followed by a ligand exchange reaction during which His 26/33, water and Met 80 are inter-exchanged as haem ligands through a thermodynamically controlled equilibrium. In the ligand exchange phase, the rate of formation of a misfolded histidine-histidine coordinated state (HH) decreases by two orders of magnitude as the pH is reduced from 5.9 to 4.5 due to the protonation of the misligated His 26/33. The activation energy barriers for the transitions from the histidine-water coordinated form (HW) to the histidine-methionine coordinated form and the HH form are 18 and 4 kcal mol-1 respectively, at pH 4.8. The activation energy barrier for protein to escape from the misligated HH to the HW form was measured to be 12 kcal mol-1, demonstrating the kinetic trapping effect of the misligated bis-histidine form. The development of the polypeptide tertiary structure near the haem is concomitant with the coordination of the native haem axial ligand.

Original languageEnglish (US)
Pages (from-to)51-56
Number of pages6
JournalNature Structural Biology
Issue number1
StatePublished - Jan 1997

ASJC Scopus subject areas

  • Structural Biology
  • Biochemistry
  • Genetics


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