Structural highlights
FunctionCCMA_ECOLI Part of the ABC transporter complex CcmAB involved in the biogenesis of c-type cytochromes; once thought to export heme, this seems not to be the case, but its exact role is uncertain. Responsible for energy coupling to the transport system. Publication Abstract from PubMedMono- and multiheme cytochromes c are post-translationally matured by the covalent attachment of heme. For this, Escherichia coli employs the most complex type of maturation machineries, the Ccm-system (for cytochrome c maturation). It consists of two membrane protein complexes, one of which shuttles heme across the membrane to a mobile chaperone that then delivers the cofactor to the second complex, an apoprotein:heme lyase, for covalent attachment. Here we report cryo-electron microscopic structures of the heme translocation complex CcmABCD from E. coli, alone and bound to the heme chaperone CcmE. CcmABCD forms a heterooctameric complex centered around the ABC transporter CcmAB that does not by itself transport heme. Our data suggest that the complex flops a heme group from the inner to the outer leaflet at its CcmBC interfaces, driven by ATP hydrolysis at CcmA. A conserved heme-handling motif (WxWD) at the periplasmic side of CcmC rotates the heme by 90 degrees for covalent attachment to the heme chaperone CcmE that we find interacting exclusively with the CcmB subunit. Architecture of the Heme-translocating CcmABCD/E complex required for Cytochrome c maturation.,Ilcu L, Denkhaus L, Brausemann A, Zhang L, Einsle O Nat Commun. 2023 Aug 25;14(1):5190. doi: 10.1038/s41467-023-40881-y. PMID:37626034[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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