The small subunit AroB of arsenite oxidase: lessons on the [2Fe-2S] Rieske protein superfamily.
Here, we describe the characterization of the [2Fe-2S] clusters of arsenite oxidases from Rhizobium sp. NT-26 and Ralstonia sp. 22. Both reduced Rieske proteins feature EPR signals similar to their homologs from Rieske-cyt b complexes, with g values at 2.027, 1.88, and 1.77. Redox titrations in a range of pH values showed that both [2Fe-2S] centers have constant E(m) values up to pH 8 at approximately +210 mV. Above this pH value, the E(m) values of both centers are pH-dependent, similar to what is observed for the Rieske-cyt b complexes. The redox properties of these two proteins, together with the low E(m) value (+160 mV) of the Alcaligenes faecalis arsenite oxidase Rieske (confirmed herein), are in line with the structural determinants observed in the primary sequences, which have previously been deduced from the study of Rieske-cyt b complexes. Since the published E(m) value of the Chloroflexus aurantiacus Rieske (+100 mV) is in conflict with this sequence analysis, we re-analyzed membrane samples of this organism and obtain a new value (+200 mV). Arsenite oxidase activity was affected by quinols and quinol analogs, which is similar to what is found with the Rieske-cyt b complexes. Together, these results show that the Rieske protein of arsenite oxidase shares numerous properties with its counterpart in the Rieske-cyt b complex. However, two cysteine residues, strictly conserved in the Rieske-cyt b-Rieske and considered to be crucial for its function, are not conserved in the arsenite oxidase counterpart. We discuss the role of these residues.
Duval
Simon
S
Laboratoire de Bioénergétique et Ingénierie des Protéines UPR 9036, Institut de Biologie Structurale et Microbiologie, CNRS, F-13402 Marseille Cedex 20, France.
Santini
Joanne M
JM
Nitschke
Wolfgang
W
Hille
Russ
R
Schoepp-Cothenet
Barbara
B
D042481:Alcaligenes faecalis / Q000201:enzymology; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D045303:Cytochromes b / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D007700:Kinetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D011090:Polyenes / Q000494:pharmacology; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D043367:Ralstonia / Q000201:enzymology*; D012231:Rhizobium / Q000201:enzymology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D000900:Anti-Bacterial Agents; D007506:Iron-Sulfur Proteins; D011090:Polyenes; D021122:Protein Subunits; D045303:Cytochromes b; C041573:stigmatellin; D010088:Oxidoreductases; C078179:arsenite oxidase