PetC1 Is the Major Rieske Iron-Sulfur Protein in the Cytochrome b6f Complex of Synechocystis sp. PCC 6803

Dirk Schneider,Stephan Berry,Thomas Volkmer,Andreas Seidler,Matthias Rögner

doi:10.1074/jbc.m406288200

Dirk Schneider, Stephan Berry + Show 3 more

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https://doi.org/10.1074/jbc.m406288200

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Abstract

Many of the completely sequenced cyanobacterial genomes contain a gene family that encodes for putative Rieske iron-sulfur proteins. The Rieske protein is one of the large subunits of the cytochrome bc-type complexes involved in respiratory and photosynthetic electron transfer. In contrast to all other subunits of this complex that are encoded by single genes, the genome of the cyanobacterium Synechocystis PCC 6803 contains three petC genes, all encoding potential Rieske subunits. Most interestingly, any of the petC genes can be deleted individually without altering the Synechocystis phenotype dramatically. In contrast, double deletion experiments revealed that petC1 and petC2 cannot be deleted in combination, whereas petC3 can be deleted together with any of the other two petC genes. Further results suggest a different physiological function for each of the Rieske proteins. Whereas PetC2 can partly replace the dominating Rieske isoform PetC1, PetC3 is unable to functionally replace either PetC1 or PetC2 and may have a special function involving a special donor with a lower redox potential than plastoquinone. A predominant role of PetC1, which is (partly) different from PetC2, is suggested by the mutational analysis and a detailed characterization of the electron transfer reactions in the mutant strains.

Highlights

In 1997 the complete DNA sequence of the mesophilic cyanobacterium Synechocystis PCC 6803 was published [1]
In contrast to all other subunits of this complex that are encoded by single genes, the genome of the cyanobacterium Synechocystis PCC 6803 contains three petC genes, all encoding potential Rieske subunits
Insertional Deletion of the Three Putative petC Genes—The three open reading frames of Synechocystis PCC 6803 encoding putative Rieske proteins were assigned petC1, petC2, and petC3 [5, 21] with the numbers given in parentheses showing the deposited name in the Cyano data base [22]

Summary

Introduction

In 1997 the complete DNA sequence of the mesophilic cyanobacterium Synechocystis PCC 6803 was published [1]. In the genomic sequence of the cyanobacterium Synechocystis PCC 6803, no genes encoding subunits of a cytochrome bc complex were found, i.e. the cytochrome b6 f complex is an essential component of both the respiratory and the photosynthetic electron transfer chain. The thylakoid membrane of cyanobacteria harbors a mixed photosynthetic and respiratory electron transport chain [13] with the plastoquinone pool receiving electrons from both photosystem II and from respiratory dehydrogenases; these are transferred via the cytochrome b6 f complex and soluble carriers (plastocyanin or cytochrome c6) to photosystem I and the terminal respiratory oxidase Due to this central function of the cytochrome b6 f complex, it is impossible to delete crucial subunits of this complex [14]. Further detailed characterization of the ⌬petC1 strain suggested that the function of petC1 can only to some degree be substituted by petC2, and the deletion of petC1 leads to a partial loss of the cytochrome b6 f complex function

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