Single Mutations That Redirect Internal Proton Transfer in the ba3 Oxidase from Thermus thermophilus
2013
Smirnova, Irina | Chang, Hsin-Yang | von Ballmoos, Christoph | Ädelroth, Pia | Gennis, Robert B. | Brzezinski, Peter
The ba₃-type cytochrome c oxidase from Thermus thermophilus is a membrane-bound proton pump. Results from earlier studies have shown that with the aa₃-type oxidases proton uptake to the catalytic site and “pump site” occurs simultaneously. However, with ba₃ oxidase the pump site is loaded before proton transfer to the catalytic site because the proton transfer to the latter is slower than that with the aa₃ oxidases. In addition, the timing of formation and decay of catalytic intermediates is different in the two types of oxidases. In the present study, we have investigated two mutant ba₃ CytcOs in which residues of the proton pathway leading to the catalytic site as well as the pump site were exchanged, Thr312Val and Tyr244Phe. Even though ba₃ CytcO uses only a single proton pathway for transfer of the substrate and “pumped” protons, the amino-acid residue substitutions had distinctly different effects on the kinetics of proton transfer to the catalytic site and the pump site. The results indicate that the rates of these reactions can be modified independently by replacement of single residues within the proton pathway. Furthermore, the data suggest that the Thr312Val and Tyr244Phe mutations interfere with a structural rearrangement in the proton pathway that is rate limiting for proton transfer to the catalytic site.
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