Abstract
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 language | English (US) |
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Pages (from-to) | 51-56 |
Number of pages | 6 |
Journal | Nature Structural Biology |
Volume | 4 |
Issue number | 1 |
DOIs | |
State | Published - Jan 1997 |
ASJC Scopus subject areas
- Structural Biology
- Biochemistry
- Genetics