TAILIEUCHUNG - Báo cáo khoa học: 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 cytochromec maturation inEscherichia 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. | ễFEBS Journal Loss of ATP hydrolysis activity by CcmAB results in loss of c-type cytochrome synthesis and incomplete processing of CcmE Olaf Christensen1 Edgar M. Harvat2 Linda Thony-Meyer1 Stuart J. Ferguson2 and Julie M. Stevens2 1 Institut fur Mikrobiologie Eidgenossische Technische Hochschule Zurich Switzerland 2 Department of Biochemistry University of Oxford UK Keywords ABC transporter CcmA CcmB CcmE cytochrome c Correspondence S. J. Ferguson and J. M. Stevens Department of Biochemistry University of Oxford South Parks Road Oxford OX1 3QU UK Fax 44 0 1865 275259 Tel 44 0 1865 275240 E-mail or Received 13 December 2006 revised 20 February 2007 accepted 2 March 2007 doi 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. The formation of the two thioether bonds between cysteine thiols and the vinyl groups of heme characteristic of c-type cytochromes requires a post-translational apparatus. Cytochromes c are found in almost all organisms and .

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