Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 30, Pages 12271-12276Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1108320108
Keywords
interaction site; ET complex; isotope edited-NMR; unidirectional ET; redox-dependent interaction
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Funding
- Japanese Ministry of Education, Culture, Sports, Science and Technology [20051002, 23121501, 16087208, 22247012]
- Japan Society for the Promotion of Science for Young Scientists
- Grants-in-Aid for Scientific Research [20051002, 22570122, 16087208, 22247012] Funding Source: KAKEN
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The final interprotein electron transfer (ET) in the mammalian respiratory chain, from cytochrome c (Cyt c) to cytochrome c oxidase (CcO) is investigated by H-1-N-15 heteronuclear single quantum coherence spectral analysis. The chemical shift perturbation in isotope-labeled Cyt c induced by addition of unlabeled CcO indicates that the hydrophobic heme periphery and adjacent hydrophobic amino acid residues of Cyt c dominantly contribute to the complex formation, whereas charged residues near the hydrophobic core refine the orientation of Cyt c to provide well controlled ET. Upon oxidation of Cyt c, the specific line broadening of N-H signals disappeared and high field H-1 chemical shifts of the N-terminal helix were observed, suggesting that the interactions of the N-terminal helix with CcO are reduced by steric constraint in oxidized Cyt c, while the chemical shift perturbations in the C-terminal helix indicate notable interactions of oxidized Cyt c with CcO. These results suggest that the overall affinity of oxidized Cyt c for CcO is significantly, but not very much weaker than that of reduced Cyt c. Thus, electron transfer is gated by dissociation of oxidized Cyt c from CcO, the rate of which is controlled by the affinity of oxidized Cyt c to CcO for providing an appropriate electron transfer rate for the most effective energy coupling. The conformational changes in Lys13 upon CcO binding to oxidized Cyt c, shown by H-1- and H-1, N-15-chemical shifts, are also expected to gate intraprotein ET by a polarity control of heme c environment.
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