title: Molecular and immunological analysis of an ABC transporter complex required for cytochrome c biogenesis.
abstract: The helABC genes are predicted to encode an ATP-binding cassette (ABC) transporter necessary for heme export for ligation in bacterial cytochrome c biogenesis. The recent discoveries of homologs of the helB and helC genes in plant mitochondrial genomes suggest this is a highly conserved transporter in prokaryotes and some eukaryotes with the HelB and HelC proteins comprising the transmembrane components. Molecular genetic analysis in the Gram-negative bacterium Rhodobacter capsulatus was used to show that the helABC and helDX genes are part of an operon linked to the secDF genes. To facilitate analysis of this transporter, strains with non-polar deletions in each gene, epitope and reporter-tagged HelABCD proteins, and antisera specific to the HelA and HelX proteins were generated. We directly demonstrate that this transporter is present in the cytoplasmic membrane as an HelABCD complex. The HelB and HelC but not HelD proteins are necessary for the binding and stability of the HelA protein, the cytoplasmic subunit containing the ATP-binding region. In addition we show that the HelA protein co-immunoprecipitates with either the HelC or HelD proteins. Thus, the HelABCD heme export complex is distinguished by the presence of four membrane-associated subunits and represents a unique subfamily of ABC transporters.
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130, USA.
authors.forename: B S
authors.initials: BS
authors.lastname: Goldman
authors.forename: D L
authors.initials: DL
authors.lastname: Beckman
authors.forename: A
authors.initials: A
authors.lastname: Bali
authors.forename: E M
authors.initials: EM
authors.lastname: Monika
authors.forename: K K
authors.initials: KK
authors.lastname: Gabbert
authors.forename: R G
authors.initials: RG
authors.lastname: Kranz
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003574:Cytochrome c Group / Q000096:biosynthesis*; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D000939:Epitopes / Q000235:genetics; D017353:Gene Deletion; D005798:Genes, Bacterial; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D009876:Operon; D010641:Phenotype; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D003574:Cytochrome c Group; D017931:DNA Primers; D004269:DNA, Bacterial; D000939:Epitopes; C109582:HelA protein, bacteria; D046911:Macromolecular Substances