Abstract
We present structural and biochemical evidence for a redox switch in the archaeal transcriptional regulator SurR of Pyrococcus furiosus, a hyperthermophilic anaerobe. P. furiosus produces H(2) during fermentation, but undergoes a metabolic shift to produce H(2) S when elemental sulfur (S(0) ) becomes available. Changes in gene expression occur within minutes of S(0) addition, and the majority of these S(0) -responsive genes are regulatory targets of SurR, a key regulator involved in primary S(0) response. SurR was shown in vitro to have dual functionality, activating transcription of some of these genes, notably the hydrogenase operons, and repressing others, including a gene-encoding sulfur reductase. This work demonstrates via biochemical and structural evidence that the activity of SurR is modulated by cysteine residues in a CxxC motif that constitutes a redox switch. Oxidation of the switch with S(0) inhibits sequence-specific DNA binding by SurR, leading to deactivation of genes related to H(2) production and derepression of genes involved in S(0) metabolism.