Topography of human cytochrome b 5 /cytochrome b 5 reductase interacting domain and redox alterations upon complex formation.

Cytochrome b ₅ is the main electron acceptor of cytochrome b ₅ reductase. The interacting domain between both human proteins has been unidentified up to date and very little is known about its redox properties modulation upon complex formation. In this article, we characterized the protein/protein interacting interface by solution NMR and molecular docking. In addition, upon complex formation, we measured an increase of cytochrome b ₅ reductase flavin autofluorescence that was dependent upon the presence of cytochrome b _5. Data analysis of these results allowed us to calculate a dissociation constant value between proteins of 0.5±0.1μM and a 1:1 stoichiometry for the complex formation. In addition, a 30mV negative shift of cytochrome b ₅ reductase redox potential in presence of cytochrome b ₅ was also measured. These experiments suggest that the FAD group of cytochrome b ₅ reductase increase its solvent exposition upon complex formation promoting an efficient electron transfer between the proteins.
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