Rhodobacter capsulatus CycH: A bipartite gene product with pleiotropic effects on the biogenesis of structurally different c-type cytochromes

Document Type

Article

Publication Date

1996

Abstract

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 c(y). 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 of 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 mediumdependent 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 CyeH2 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.

Publication Title

Journal of Bacteriology

Volume

178

First Page

5279

Last Page

5290

Comments

This article was published in Journal of Bacteriology, Volume 178, Issue 17, Pages 5279-5290.

The published version is available at http://jb.asm.org/content/178/17/5279.abstract .

Copyright © 1996 ASM.

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