Abstract
Cell metabolism relies on energy transduction usually performed by complex membrane-spanning proteins that couple different chemical processes, e.g. electron and proton transfer in proton-pumps. There is great interest in determining at the molecular level the structural details that control these energy transduction events, particularly those involving multiple electrons and protons, because tight control is required to avoid the production of dangerous reactive intermediates. Tetraheme cytochrome c(3) is a small soluble and monomeric protein that performs a central step in the bioenergetic metabolism of sulfate reducing bacteria, termed "proton-thrusting," linking the oxidation of molecular hydrogen with the reduction of sulfate. The mechano-chemical coupling involved in the transfer of multiple electrons and protons in cytochrome c(3) from Desulfovibrio desulfuricans ATCC 27774 is described using results derived from the microscopic thermodynamic characterization of the redox and acid-base centers involved, crystallographic studies in the oxidized and reduced states of the cytochrome, and theoretical studies of the redox and acid-base transitions. This proton-assisted two-electron step involves very small, localized structural changes that are sufficient to generate the complex network of functional cooperativities leading to energy transduction, while using molecular mechanisms distinct from those established for other Desulfovibrio sp. cytochromes from the same structural family.
Highlights
Recent developments in techniques of structural biology have opened the way for probing the mechanisms used by biological macromolecules involved in energy transduction at the molecular level
The mechanochemical coupling involved in the transfer of multiple electrons and protons in cytochrome c3 from Desulfovibrio desulfuricans ATCC 27774 is described using results derived from the microscopic thermodynamic characterization of the redox and acid-base centers involved, crystallographic studies in the oxidized and reduced states of the cytochrome, and theoretical studies of the redox and acid-base transitions
This proton-assisted two-electron step involves very small, localized structural changes that are sufficient to generate the complex network of functional cooperativities leading to energy transduction, while using molecular mechanisms distinct from those established for other Desulfovibrio sp. cytochromes from the same structural family
Summary
Recent developments in techniques of structural biology have opened the way for probing the mechanisms used by biological macromolecules involved in energy transduction at the molecular level. The analysis integrates data derived from the microscopic thermodynamic characterization of the hemes and acid-base centers (6), the structures obtained by x-ray crystallography in the oxidized and reduced states, and theoretical studies based on these structures. These data provide a coherent description of the mechanism that enables the efficient coupling of the transfer of two electrons with protons in the physiological pH range. The thermodynamically coupled transfer of electrons and protons observed in the soluble cytochromes c3 has been termed “proton-thrusting” because it parallels the linkage between redoxand proton-transfer mechanisms of larger, membrane-embedded protein complexes involved in proton pumping (10)
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