Apd1, a cytosolic yeast protein, and Aim32, its counterpart in the mitochondrial matrix, have a C-terminal thioredoxinlike ferredoxin domain and a widely divergent N-terminal domain. These proteins are found in bacteria, plants, fungi and unicellular pathogenic eukaryotes, but not in Metazoa. Our chemogenetic experiments demonstrate that the highly conserved cysteine and histidine residues within the C-X8-C-X24-75-H-X-G-G-H motif of the TLF domain of Apd1 and Aim32 proteins are essential for viability upon treatment of yeast cells with the redox potentiators gallobenzophenone or pyrogallol, respectively. UV-Vis, EPR and Mössbauer spectroscopy of purified wild type Apd1 and three His to Cys variants demonstrated that Cys207 and Cys216 are the ligands of the ferric ion and His255 and His259 are the ligands of the reducible iron ion of the [2Fe-2S] 2+/1+ cluster. The [2Fe-2S] center of Apd1 (Em,7 = 164±5 mV, pKox1,27.9±0.1 and 9.7±0.1) differs from both dioxygenase (Em,7  150 mV, pKox1,2=9.8 and 11.5) and cytochrome bc1/b6f Rieske clusters (Em,7  +300 mV, pKox1,2= 7.7 and 9.8). Apd1 and its engineered variants represent an unprecedented flexible system for which a stable [2Fe-2S] cluster with two histidine ligands, (two different) single histidine ligands or only cysteinyl ligands is possible in the same protein fold. Our results define a remarkable example of convergent evolution of [2Fe-2S] cluster containing proteins with bis-histidinyl coordination and proton-coupled electron transfer. Strain Plasmid Gallobenzophenone 25 µM none 50 µM empty Aim32 ∆aim32 Wild type Apd1 empty ∆apd1 empty Aim32 Apd1 a empty ∆sod2 Strain Plasmid ∆sod2/ Δaim32 empty Aim32 Apd1 Pyrogallol 25 µM none 50 µM empty Aim32 ∆aim32 Wild type

Apd1, a cytosolic yeast protein, and Aim32, its counterpart in the mitochondrial matrix, have a C-terminal thioredoxinlike ferredoxin domain and a widely divergent N-terminal domain. These proteins are found in bacteria, plants, fungi and unicellular pathogenic eukaryotes, but not in Metazoa. Our chemogenetic experiments demonstrate that the highly conserved cysteine and histidine residues within the C-X8-C-X24-75-H-X-G-G-H motif of the TLF domain of Apd1 and Aim32 proteins are essential for viability upon treatment of yeast cells with the redox potentiators gallobenzophenone or pyrogallol, respectively. UV-Vis, EPR and Mössbauer spectroscopy of purified wild type Apd1 and three His to Cys variants demonstrated that Cys207 and Cys216 are the ligands of the ferric ion and His255 and His259 are the ligands of the reducible iron ion of the [2Fe-2S]2+/1+ cluster. The [2Fe-2S] center of Apd1 (Em,7 = -164±5 mV, pKox1,2=7.9±0.1 and 9.7±0.1) differs from both dioxygenase (Em,7 ≈ -150 mV, pKox1,2=9.8 and 11.5) and cytochrome bc1/b6f Rieske clusters (Em,7 ≈ +300 mV, pKox1,2= 7.7 and 9.8). Apd1 and its engineered variants represent an unprecedented flexible system for which a stable [2Fe-2S] cluster with two histidine ligands, (two different) single histidine ligands or only cysteinyl ligands is possible in the same protein fold. Our results define a remarkable example of convergent evolution of [2Fe-2S] cluster containing proteins with bis-histidinyl coordination and proton-coupled electron transfer.<br>

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Apd1, a cytosolic yeast protein, and Aim32, its counterpart in the mitochondrial matrix, have a C-terminal thioredoxinlike ferredoxin domain and a widely divergent N-terminal domain. These proteins are found in bacteria, plants, fungi and unicellular pathogenic eukaryotes, but not in Metazoa. Our chemogenetic experiments demonstrate that the highly conserved cysteine and histidine residues within the C-X8-C-X24-75-H-X-G-G-H motif of the TLF domain of Apd1 and Aim32 proteins are essential for viability upon treatment of yeast cells with the redox potentiators gallobenzophenone or pyrogallol, respectively. UV-Vis, EPR and Mössbauer spectroscopy of purified wild type Apd1 and three His to Cys variants demonstrated that Cys207 and Cys216 are the ligands of the ferric ion and His255 and His259 are the ligands of the reducible iron ion of the [2Fe-2S]2+/1+ cluster. The [2Fe-2S] center of Apd1 (Em,7 = -164±5 mV, pKox1,2=7.9±0.1 and 9.7±0.1) differs from both dioxygenase (Em,7 ≈ -150 mV, pKox1,2=9.8 and 11.5) and cytochrome bc1/b6f Rieske clusters (Em,7 ≈ +300 mV, pKox1,2= 7.7 and 9.8). Apd1 and its engineered variants represent an unprecedented flexible system for which a stable [2Fe-2S] cluster with two histidine ligands, (two different) single histidine ligands or only cysteinyl ligands is possible in the same protein fold. Our results define a remarkable example of convergent evolution of [2Fe-2S] cluster containing proteins with bis-histidinyl coordination and proton-coupled electron transfer.<br>