2-OXOACID-FERREDOXIN OXIDOREDUCTASE FROM THE THERMOACIDOPHILIC ARCHAEON, SULFOLOBUS SP STRAIN-7

The purified 2-oxoacid:ferredoxin oxidoreductase of a thermoacidophili c and aerobic crenarchaeote, Sulfolobus sp, strain 7, consists of 70-k Da alpha and 37-kDa beta subunits, and contains one thiamine pyrophosp hate (TPP), one [4Fe-4S](2+,1+) cluster, and two magnesium atoms per a lpha beta structure, It exhibits a broad substrate specificity toward 2-oxoacids such as 2-oxoglutarate, 2-oxobutyrate, and pyruvate, The ge ne encoding the archaeal oxidoreductase was cloned, and the two open r eading frames encoding the alpha (632 amino acids) and beta subunits ( 305 amino acids), respectively, were sequenced, Careful sequence align ment revealed several consensus motifs of this enzyme family, as well as possible cofactor binding residues of the Sulfolobus enzyme, This n ew structural information also indicates that (i) several genetic fusi ons and reorganization of the early, possibly alpha beta gamma delta-t ype enzyme similar to those from hyperthermophiles have taken place du ring evolution of the 2-oxoacid:ferredoxin (flavodoxin) oxidoreductase superfamily, which might have occurred in different ways in early aer obic archaea and early anaerobic bacteria, and that (ii) enzymes with different subunit compositions should have an essentially similar cata lytic mechanism with one TPP and at least one [4Fe-4S] cluster as the minimal set of redox centers.