The C-terminal flexible domain of the heme chaperone CcmE is important but not essential for its function.
CcmE is a heme chaperone active in the cytochrome c maturation pathway of Escherichia coli. It first binds heme covalently to strictly conserved histidine H130 and subsequently delivers it to apo-cytochrome c. The recently solved structure of soluble CcmE revealed a compact core consisting of a beta-barrel and a flexible C-terminal domain with a short alpha-helical turn. In order to elucidate the function of this poorly conserved domain, CcmE was truncated stepwise from the C terminus. Removal of all 29 amino acids up to crucial histidine 130 did not abolish heme binding completely. For detectable transfer of heme to type c cytochromes, only one additional residue, D131, was required, and for efficient cytochrome c maturation, the seven-residue sequence (131)DENYTPP(137) was required. When soluble forms of CcmE were expressed in the periplasm, the C-terminal domain had to be slightly longer to allow detection of holo-CcmE. Soluble full-length CcmE had low activity in cytochrome c maturation, indicating the importance of the N-terminal membrane anchor for the in vivo function of CcmE.
Enggist
Elisabeth
E
Institut für Mikrobiologie, Departement Biologie, Eidgenössische Technische Hochschule, CH-8092 Zürich, Switzerland.
Thöny-Meyer
Linda
L
D000595:Amino Acid Sequence; D001051:Apoenzymes; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D019897:Periplasm / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013057:Spectrum Analysis / Q000379:methods
D001051:Apoenzymes; D001425:Bacterial Outer Membrane Proteins; C115384:CcmE protein, E coli; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D018832:Molecular Chaperones; D006418:Heme