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Fast folding of cytochrome c
1Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760, USA.
Protein Science : a Publication of the Protein Society
|March 1, 1997
Summary
Non-native histidine-heme ligation in iso-2 cytochrome c slows protein folding. A double mutant protein lacking these non-native ligands folds significantly faster, supporting this kinetic barrier hypothesis.
Area of Science:
- Biochemistry
- Protein folding dynamics
- Cytochrome c structure-function relationships
Background:
- Native iso-2 cytochrome c features His 18 and Met 80 coordinating the heme iron.
- During unfolding, Met 80 is displaced by His 33 or His 39, forming non-native heme ligation.
Purpose of the Study:
- To investigate if non-native histidine-heme ligation impedes the fast folding of iso-2 cytochrome c.
- To quantify the folding rate differences between native and mutant iso-2 cytochrome c.
Main Methods:
- Construction of a double mutant (H33N,H39K) iso-2 cytochrome c to prevent non-native histidine-heme coordination.
- Comparative kinetic analysis of protein folding rates for wild-type and mutant iso-2 cytochrome c.
Main Results:
- The H33N,H39K double mutant exhibited significantly accelerated folding rates (gamma = 14-26 ms) compared to wild-type iso-2 cytochrome c (gamma = 200-1,100 ms).
- This demonstrates that the absence of non-native histidine-heme bonds facilitates faster protein folding.
Conclusions:
- Non-native histidine-heme ligation acts as a kinetic barrier, slowing down the folding process of iso-2 cytochrome c.
- The folding pathway likely involves a limited number of partially folded intermediates, suggesting an efficient folding mechanism when barriers are removed.