Isolation and characterization of a rubredoxin and a two-(4Fe-4S) ferredoxin from Thermodesulfobacterium commune

Abstract

Two non-heme iron proteins, ferredoxin and rubredoxin, have been isolated from the thermophilic non-sporeforming sulfate-reducer Thermodesulfobacterium commune. In most respects, the rubredoxin is similar to the corresponding mesophile proteins from other anaerobic bacteria but it differs by its higher content of proline residues. Native ferredoxin from T. commune is a dimer comprising two identical subunits of approx. 7000 molecular weight. Its absorption spectrum exhibits two maxima at 385 nm (29 500 M −1 · cm −1) and 280 nm (36 100 M −1 · cm −1) and its A 385 A 280 absorbance ratio is 0.82. The protein contains 8 atoms each of iron and labile sulfur per molecule. The absorption at 385 nm and the content of iron of the protein are in agreement with the presence of two (4Fe-4S) clusters in T. commune ferredoxin. Its amino acid composition shows the presence of six cysteine residues and is characterized by the absence of histidine and a high content of aromatic residues. The N-terminal amino acid sequence of T. commune ferredoxin has been established. The comparison of amino acid sequences shows that it presents more homology with the one-(4Fe-4S) ferredoxin from Clostridium thermoaceticum than with the two-(4Fe-4S) ferredoxin from Desulfovibrio desulfuricans Norway. T. commune ferredoxin shows thermal stability and retains its full activity in the phosphoroclastic reaction after treatment at 70°C. The protein exhibits sensitivity towards oxygen at 25°C.