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Structural Changes and Proton Transfer in Cytochrome c Oxidase.

Jóhanna Vilhjálmsdóttir1, Ann-Louise Johansson1, Peter Brzezinski1

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Cytochrome c oxidase couples electron transfer to proton pumping via structural changes near heme a. Modifying Ser425 impacts proton pathways, linking redox changes to proton transfer rates.

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Area of Science:

  • Biochemistry
  • Bioenergetics
  • Structural Biology

Background:

  • Cytochrome c oxidase facilitates electron transfer from cytochrome c to O2, coupled with transmembrane proton pumping.
  • This process is crucial for maintaining the proton electrochemical gradient essential for ATP synthesis.
  • The precise mechanism linking electron transfer to proton translocation remains unclear, but likely involves redox-induced structural changes.

Purpose of the Study:

  • To investigate the functional impact of redox-induced structural changes near heme a on proton pumping.
  • To explore the role of specific residues, such as Ser425, in coupling electron transfer to proton translocation.
  • To elucidate the connection between structural dynamics and proton pathway modulation.

Main Methods:

  • Site-directed mutagenesis was employed to modify residue Ser425 in cytochrome c oxidase.
  • Time-resolved spectroscopy was utilized to monitor coupled electron-proton transfer reactions.
  • X-ray crystallography data informed the investigation of structural changes at residues 423-425.

Main Results:

  • Modification of Ser425 led to observable functional effects on proton pumping-associated reaction steps.
  • The structural change at position 425 was found to propagate to the D proton pathway.
  • Data suggest a direct link between redox events at heme a and the regulation of intramolecular proton transfer rates.

Conclusions:

  • Redox-induced structural changes near heme a play a critical role in cytochrome c oxidase function.
  • The D proton pathway is sensitive to structural modifications, indicating its involvement in proton translocation.
  • These findings provide insights into the mechanism of proton pumping and its regulation by electron transfer.