title: A 35 kDa NAD(P)H oxidase previously isolated from the archaeon Sulfolobus solfataricus is instead a thioredoxin reductase.
abstract: A thioredoxin reductase (TrxR) has been identified in the hyperthermophilic archaeon Sulfolobus solfataricus (Ss). This enzyme is a homodimeric flavoprotein that was previously identified as NADH oxidase in the same micro-organism ('Biotechnol. Appl. Biochem. 23 (1996) 47'). The primary structure of SsTrxR is made of 323 amino acid residues and contains two putative betaalphabeta regions for the binding of FAD, and a NADP(H) binding consensus sequence in the proximity of a CXXC motif. These findings indicate that SsTrxR is structurally related to the class II of the pyridine nucleotide-disulphide oxidoreductases family. Moreover, the enzyme exhibits a NADP(H) dependent thioredoxin reductase activity requiring the presence of FAD. Surprisingly, the reductase activity of SsTrxR is reduced in the presence of a specific inhibitor of mammalian TrxR. This finding demonstrates that the archaeal enzyme, although structurally related to eubacterial TrxR, is functionally closer to eukaryal enzymes. Experimental evidences indicate that a disulphide bridge is required for the reductase but also for the NADH oxidase activity of the enzyme. These results are further supported by the significantly reduced activities exerted by the C147A mutant. The integrity of the CXXC motif is also involved in the stability of the enzyme.
authors.affiliation: Dipartimento di Biochimica e Biotecnologie Mediche, Università di Napoli Federico II, via S. Pansini 5, I-80131 Napoli, Italia.
authors.forename: M R
authors.initials: MR
authors.lastname: Ruocco
authors.forename: A
authors.initials: A
authors.lastname: Ruggiero
authors.forename: L
authors.initials: L
authors.lastname: Masullo
authors.forename: P
authors.initials: P
authors.lastname: Arcari
authors.forename: M
authors.initials: M
authors.lastname: Masullo
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001105:Archaea / Q000201:enzymology* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D016384:Consensus Sequence; D003545:Cysteine / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry; D004795:Enzyme Stability; D005182:Flavin-Adenine Dinucleotide / Q000032:analysis; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D009247:NADH, NADPH Oxidoreductases / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D019255:NADPH Oxidases; D017386:Sequence Homology, Amino Acid; D048229:Sulfolobus solfataricus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D013696:Temperature; D013880:Thioredoxin-Disulfide Reductase / Q000032:analysis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D004220:Disulfides; D005182:Flavin-Adenine Dinucleotide; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D013880:Thioredoxin-Disulfide Reductase; D003545:Cysteine