Abstract
The CcmH protein of Escherichia coli is encoded by the last gene of the ccm gene cluster required for cytochrome c maturation. A mutant in which the entire ccmH gene was deleted failed to synthesize both indigenous and foreign c-type cytochromes. However, deletion of the C-terminal hydrophilic domain homologous to CycH of other gram-negative bacteria affected neither the biogenesis of indigenous c-type cytochromes nor that of the Bradyrhizobium japonicum cytochrome c 550. This confirmed that only the N-terminal domain containing a conserved CXXC motif is required in E. coli. PhoA fusion analysis showed that this domain is periplasmic. Site-directed mutagenesis of the cysteines of the CXXC motif revealed that both cysteines are required for cytochrome c maturation during aerobic growth, whereas only the second cysteine is required for cytochrome c maturation during anaerobic growth. The deficiency of the point mutants was complemented when 2-mercapto-ethanesulfonic acid was added to growing cells; other thiol compounds did not stimulate cytochrome c formation in these strains. We propose a model for the reaction sequence in which CcmH keeps the heme binding site of apocytochrome c in a reduced form for subsequent heme ligation.
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Received: 7 September 1998 / Accepted: 15 November 1998
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Fabianek, R., Hofer, T. & Thöny-Meyer, L. Characterization of the Escherichia coli CcmH protein reveals new insights into the redox pathway required for cytochrome c maturation. Arch Microbiol 171, 92–100 (1999). https://doi.org/10.1007/s002030050683
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DOI: https://doi.org/10.1007/s002030050683