Function and Regulation of Ferredoxins in the Cyanobacterium, Synechocystis PCC6803: Recent Advances.

Corinne Cassier-Chauvat,Franck Chauvat

doi:10.3390/life4040666

Abstract

Ferredoxins (Fed), occurring in most organisms, are small proteins that use their iron-sulfur cluster to distribute electrons to various metabolic pathways, likely including hydrogen production. Here, we summarize the current knowledge on ferredoxins in cyanobacteria, the prokaryotes regarded as important producers of the oxygenic atmosphere and biomass for the food chain, as well as promising cell factories for biofuel production. Most studies of ferredoxins were performed in the model strain, Synechocystis PCC6803, which possesses nine highly-conserved ferredoxins encoded by monocistronic or operonic genes, some of which are localized in conserved genome regions. Fed1, encoded by a light-inducible gene, is a highly abundant protein essential to photosynthesis. Fed2-Fed9, encoded by genes differently regulated by trophic conditions, are low-abundant proteins that play prominent roles in the tolerance to environmental stresses. Concerning the selectivity/redundancy of ferredoxin, we report that Fed1, Fed7 and Fed9 belong to ferredoxin-glutaredoxin-thioredoxin crosstalk pathways operating in the protection against oxidative and metal stresses. Furthermore, Fed7 specifically interacts with a DnaJ-like protein, an interaction that has been conserved in photosynthetic eukaryotes in the form of a composite protein comprising DnaJ- and Fed7-like domains. Fed9 specifically interacts with the Flv3 flavodiiron protein acting in the photoreduction of O2 to H2O.

Highlights

Ferredoxins (Fed) are small, mostly acidic, soluble proteins found ubiquitously in biological organisms
We summarize what is known about the function and regulation of ferredoxins in cyanobacteria, emphasizing the unicellular model cyanobacterium, Synechocystis PCC6803, where the Fed proteins have been mostly studied
It is important to analyze the selectivity/redundancy of ferredoxins in cyanobacteria, because these enzymes play crucial roles in the growth and/or tolerance to environmental stresses of these fascinating organisms, which produce a large part of the oxygen and biomass for the food chain and have high biotechnological interest

Summary

Introduction

Ferredoxins (Fed) are small, mostly acidic, soluble proteins found ubiquitously in biological organisms. They possess a highly negative redox potential and use their iron-sulfur cluster to act as electron distributors in various metabolic pathways. Cyanobacteria possess various [2Fe-2S] and [4Fe-4S] Feds that have received less attention than Fed, so far [2]. The interest in these ferredoxins has increased by the recent in vitro indications that one of these Fed can directly reduce NiFe-hydrogenase, which can produce hydrogen in some conditions [4]. We summarize what is known about the function and regulation of ferredoxins in cyanobacteria, emphasizing the unicellular model cyanobacterium, Synechocystis PCC6803, where the Fed proteins have been mostly studied

The Nine Ferredoxins of Synechocystis Are Highly Conserved in Cyanobacteria

Conclusions