Unexpected Elevated Production of Aquifex aeolicus Cytochrome c₅₅₅ in Escherichia coli Cells Lacking Disulfide Oxidoreductases

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Mutant strains of Escherichia coli lacking DsbA, DsbB, or DsbD (proteins required for disulfide bond formation in the periplasm) did not produce mitochondrial or chloroplast cytochromes c, as previously observed for bacterial ones. Unexpectedly, however, cytochrome c₅₅₅ (AA c₅₅₅) from a hyperthermophile, Aquifex aeolicus, was produced in the E. coli periplasm without Dsb proteins, three times more than with them. These results indicate that the Dsb proteins are not necessarily required for AA c₅₅₅ production in E. coli, possibly because of hyperthermophilic origin compared with the others.