Rhodobacter capsulatus CycH: a bipartite gene product with pleiotropic effects on the biogenesis of structurally different c-type cytochromes.
While searching for components of the soluble electron carrier (cytochrome c2)-independent photosynthetic (Ps) growth pathway in Rhodobacter capsulatus, a Ps- mutant (FJM13) was isolated from a Ps+ cytochrome c2-strain. This mutant could be complemented to Ps+ growth by cycA encoding the soluble cytochrome c2 but was unable to produce several c-type cytochromes. Only cytochrome c1 of the cytochrome bc1 complex was present in FJM13 cells grown on enriched medium, while cells grown on minimal medium contained at various levels all c-type cytochromes, including the membrane-bound electron carrier cytochrome cy. Complementation of FJM13 by a chromosomal library lacking cycA yielded a DNA fragment which also complemented a previously described Ps- mutant, MT113, known to lack all c-type cytochromes. Deletion and DNA sequence analyses revealed an open reading frame homologous to cycH, involved in cytochrome c biogenesis. The cycH gene product (CycH) is predicted to be a bipartite protein with membrane-associated amino-terminal (CycH1) and periplasmic carboxyl-terminal (CycH2) subdomains. Mutations eliminating CyCH drastically decrease the production or all known c-type cytochromes. However, mutations truncating only its CycH2 subdomain always produce cytochrome c1 and affect the presence of other cytochromes to different degrees in a growth medium-dependent manner. Thus, the subdomain CycH1 is sufficient for the proper maturation of cytochrome c1 which is the only known c-type cytochrome anchored to the cytoplasmic membrane by its carboxyl terminus, while CycH2 is required for efficient biogenesis of other c-type cytochromes. These findings demonstrate that the two subdomains of CycH play different roles in the biogenesis of topologically distinct c-type cytochromes and reconcile the apparently conflicting data previously obtained for other species.
Lang
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Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia 19104-6018, USA.
Jenney
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Daldal
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D003574:Cytochrome c Group / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D003575:Cytochromes c1 / Q000096:biosynthesis; D045362:Cytochromes c2; D004269:DNA, Bacterial; D017353:Gene Deletion; D005816:Genetic Complementation Test; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics; D014176:Protein Biosynthesis; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D003574:Cytochrome c Group; D004269:DNA, Bacterial; D008565:Membrane Proteins; D010446:Peptide Fragments; D003575:Cytochromes c1; D045362:Cytochromes c2; C017165:cytochrome c(3)