title: Overproduction of CcmG and CcmFH(Rc) fully suppresses the c-type cytochrome biogenesis defect of Rhodobacter capsulatus CcmI-null mutants.
abstract: Gram-negative bacteria like Rhodobacter capsulatus use intertwined pathways to carry out the posttranslational maturation of c-type cytochromes (Cyts). This periplasmic process requires at least 10 essential components for apo-Cyt c chaperoning, thio-oxidoreduction, and the delivery of heme and its covalent ligation. One of these components, CcmI (also called CycH), is thought to act as an apo-Cyt c chaperone. In R. capsulatus, CcmI-null mutants are unable to produce c-type Cyts and thus sustain photosynthetic (Ps) growth. Previously, we have shown that overproduction of the putative heme ligation components CcmF and CcmH(Rc) (also called Ccl1 and Ccl2) can partially bypass the function of CcmI on minimal, but not on enriched, media. Here, we demonstrate that either additional overproduction of CcmG (also called HelX) or hyperproduction of CcmF-CcmH(Rc) is needed to completely overcome the role of CcmI during the biogenesis of c-type Cyts on both minimal and enriched media. These findings indicate that, in the absence of CcmI, interactions between the heme ligation and thioreduction pathways become restricted for sufficient Cyt c production. We therefore suggest that CcmI, along with its apo-Cyt chaperoning function, is also critical for the efficacy of holo-Cyt c formation, possibly via its close interactions with other components performing the final heme ligation steps during Cyt c biogenesis.
authors.affiliation: Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Carsten
authors.initials: C
authors.lastname: Sanders
authors.forename: Meenal
authors.initials: M
authors.lastname: Deshmukh
authors.forename: Doniel
authors.initials: D
authors.lastname: Astor
authors.forename: Robert G
authors.initials: RG
authors.lastname: Kranz
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis*; D045304:Cytochromes c / Q000096:biosynthesis*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D016354:Rhodobacter capsulatus / Q000235:genetics* / Q000378:metabolism*; D013489:Suppression, Genetic
chemical_list: D001426:Bacterial Proteins; D045304:Cytochromes c