Structure of cytochrome c′: a dimeric, high-spin haem protein


The bacterial cytochromes c′ (ref. 1) occur in various photosynthetic and denitrifying bacteria, where they are presumed to function in electron transport2. Most cytochromes c′ are isolated as dimeric molecules composed of two identical subunits of 14,000 molecular weight (MW), with each polypeptide chain incorporating a protohaem IX prosthetic group covalently bound through thioether linkages formed by condensation of two cysteine side chains with the haem vinyl groups3. Although a similar mode of covalent haem attachment is found in members of the well studied mitochondrial cytochrome c family4, the cytochromes c′ are, in contrast, high-spin haem proteins (hence the prime designation) which bind neutral ligands5, characteristic properties generally associated with members of the oxygen-binding globin family6. Here we present a preliminary structural description of the cytochrome c′ derived from the photosynthetic, purple non-sulphur bacterium Rhodospirillum molischianum, and show that it bears little structural resemblance to members of either the cytochrome c or globin structural families. The cytochrome c′ monomer structure is, instead, principally organized as a left-twisted, 4-α-helical bundle, a structural motif previously observed in several other sequentially and functionally unrelated proteins7 13.

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Weber, P., Bartsch, R., Cusanovich, M. et al. Structure of cytochrome c′: a dimeric, high-spin haem protein. Nature 286, 302–304 (1980).

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