Structural differences between mesophilic, moderately thermophilic and extremely thermophilic protein subunits: results of a comprehensive survey

A ferredoxin has been purified from one of the most ancient and most thermophilic bacteria known, Thermotoga maritima, which grows up to 90 degrees C. The reduced protein (M(r) approx. 6300) contains a single S = 1/2 [4Fe-4S]1+ cluster with complete cysteinyl ligation, and was unaffected after incubation at 95 degrees C for 12 h. It functioned as an electron carrier for T. maritima pyruvate oxidoreductase. Remarkably, the properties and amino acid sequence of this hyperthermophilic bacterial protein are much more similar to those of ferredoxins from hyperthermophilic archaea, rather than ferredoxins from mesophilic and moderately thermophilic bacteria.