Cysteine Mutational Studies Provide Insight into a Thiol-Based Redox Switch Mechanism of Metal and DNA Binding in FurA from Anabaena sp. PCC 7120.

AIMS

The ferric uptake regulator (Fur) is the main transcriptional regulator of genes involved in iron homeostasis in most prokaryotes. FurA from Anabaena sp. PCC 7120 contains five cysteine residues, four of them arranged in two redox-active CXXC motifs. The protein needs not only metal but also reducing conditions to remain fully active in vitro. Through a mutational study of the cysteine residues present in FurA, we have investigated their involvement in metal and DNA binding.

RESULTS

Residue C that belongs to a conserved CXXC motif plays an essential role in both metal and DNA binding activities in vitro. Substitution of C by serine impairs DNA and metal binding abilities of FurA. Isothermal titration calorimetry measurements show that the redox state of C is responsible for the protein ability to coordinate the metal corepressor. Moreover, the redox state of C varies with the presence or absence of C or C, suggesting that the environments of these cysteines are mutually interdependent.

INNOVATION

We propose that C is part of a thiol/disulfide redox switch that determines FurA ability to bind the metal corepressor.

CONCLUSION

This mechanism supports a novel feature of a Fur protein that emerges as a regulator, which connects the response to changes in the intracellular redox state and iron management in cyanobacteria. Antioxid. Redox Signal. 00, 000-000.