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The proteins CcmA and CcmB have long been known to be essential for cytochrome c maturation in Escherichia coli. We have purified a complex of these proteins, and found it to have ATP hydrolysis activity. CcmA, which has the features of a soluble ATP hydrolysis subunit, is found in a membrane-bound complex only when CcmB is present in the membrane. Mutation of the Walker A motif in CcmA(K40D) results in loss of the in vitro ATPase activity and in loss of cytochrome c biogenesis in vivo. The same mutation does not prevent covalent attachment of heme to the heme chaperone CcmE, but holo-CcmE is, for some unidentified reason, incompetent for heme transfer to an apocytochrome c or for release into the periplasm as a soluble variant. Addition of exogenous heme to heme-permeable E. coli with a ccmA deletion did not restore cytochrome c production. Our results suggest a role for CcmAB in the handling of heme by CcmE, which is chemically complex and involves an unusual histidine-heme covalent bond.

Original publication




Journal article



Publication Date





2322 - 2332


ATP-Binding Cassette Transporters, Adenosine Triphosphate, Amino Acid Motifs, Aspartic Acid, Bacterial Outer Membrane Proteins, Cytochromes c, Escherichia coli, Escherichia coli Proteins, Heme, Hemeproteins, Histidine, Hydrolysis, Lysine, Mutagenesis, Site-Directed, Protein Processing, Post-Translational, Protein Subunits, Sequence Deletion