The timing of heme incorporation into yeast cytochrome b

• During oxidative phosphorylation electrons are transferred from NADH and succinate to the final electron acceptor oxygen by the complexes of the respiratory chain. These complexes carry redox active prosthetic groups that allow the transfer of electrons. Cytochrome b of the bc1 complex is encoded in the mitochondrial genome and acquires two heme b cofactors during its biogenesis. In this work we aimed to understand the mechanism and timing of cytochrome b hemylation. We provide evidence that cytochrome b present in the first bc1 complex assembly intermediate that contains the assembly factors Cbp3-Cbp6 and Cbp4 carries heme. This demonstrates that heme acquisition occurs very early during cytochrome b biogenesis. Moreover, by analyzing cytochrome b mutants lacking either of the two heme moieties, we reveal an obligate order of heme insertion into cytochrome b and suggest an incorporation mode from the intermembrane space. We propose a model in which Cbp3-Cbp6 keeps cytochrome b in a conformation allowing heme acquisition. Upon heme insertion, cytochrome b most likely undergoes a conformational change that enables binding of Cbp4, a pre-requisite for further assembly. Cbp4 thus might exhibit a proofreading function in hemylation.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

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