title: Evolutionary domain fusion expanded the substrate specificity of the transmembrane electron transporter DsbD.
abstract: Modular organization of proteins has been postulated as a widely used strategy for protein evolution. The multidomain transmembrane protein DsbD catalyzes the transfer of electrons from the cytoplasm to the periplasm of Escherichia coli. Most bacterial species do not have DsbD, but instead their genomes encode a much smaller protein, CcdA, which resembles the central hydrophobic domain of DsbD. We used reciprocal heterologous complementation assays between E.coli and Rhodobacter capsulatus to show that, despite their differences in size and structure, DsbD and CcdA are functional homologs. While DsbD transfers reducing potential to periplasmic protein disulfide bond isomerases and to the cytochrome c thioreduction pathway, CcdA appears to be involved only in cytochrome c biogenesis. Our findings strongly suggest that, by the acquisition of additional thiol-redox active domains, DsbD expanded its substrate specificity.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Federico
authors.initials: F
authors.lastname: Katzen
authors.forename: Meenal
authors.initials: M
authors.lastname: Deshmukh
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
authors.forename: Jon
authors.initials: J
authors.lastname: Beckwith
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003574:Cytochrome c Group / Q000096:biosynthesis; D004579:Electron Transport / Q000235:genetics / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D005813:Genes, Synthetic; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010802:Phylogeny; D019704:Protein Disulfide-Isomerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C068355:CcdA protein, Bacteria; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D013438:Sulfhydryl Compounds; D019704:Protein Disulfide-Isomerases