Loss of ATP hydrolysis activity by CcmAB results in loss of c-type cytochrome synthesis and incomplete processing of CcmE.
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.
Christensen
Olaf
O
Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Zürich, Switzerland.
Harvat
Edgar M
EM
Thöny-Meyer
Linda
L
Ferguson
Stuart J
SJ
Stevens
Julie M
JM
D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs / Q000235:genetics; D001224:Aspartic Acid / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D045304:Cytochromes c / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006420:Hemeproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism; D006868:Hydrolysis; D008239:Lysine / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D011499:Protein Processing, Post-Translational / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion
D018528:ATP-Binding Cassette Transporters; D001425:Bacterial Outer Membrane Proteins; C118373:CcmA protein, bacteria; C513740:CcmB protein, E coli; C115384:CcmE protein, E coli; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D021122:Protein Subunits; D001224:Aspartic Acid; D006418:Heme; D006639:Histidine; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D008239:Lysine