title: A Novel F420-dependent Thioredoxin Reductase Gated by Low Potential FAD: A TOOL FOR REDOX REGULATION IN AN ANAEROBE.
abstract: A recent report suggested that the thioredoxin-dependent metabolic regulation, which is widespread in all domains of life, existed in methanogenic archaea about 3.5 billion years ago. We now show that the respective electron delivery enzyme (thioredoxin reductase, TrxR), although structurally similar to flavin-containing NADPH-dependent TrxRs (NTR), lacked an NADPH-binding site and was dependent on reduced coenzyme F420(F420H2), a stronger reductant with a mid-point redox potential (E'0) of -360 mV; E'0of NAD(P)H is -320 mV. Because F420is a deazaflavin, this enzyme was named deazaflavin-dependent flavin-containing thioredoxin reductase (DFTR). It transferred electrons from F420H2to thioredoxin via protein-bound flavin; Kmvalues for thioredoxin and F420H2were 6.3 and 28.6 μm, respectively. The E'0of DFTR-bound flavin was approximately -389 mV, making electron transfer from NAD(P)H or F420H2to flavin endergonic. However, under high partial pressures of hydrogen prevailing on early Earth and present day deep-sea volcanoes, the potential for the F420/F420H2pair could be as low as -425 mV, making DFTR efficient. The presence of DFTR exclusively in ancient methanogens and mostly in the early Earth environment of deep-sea volcanoes and DFTR's characteristics suggest that the enzyme developed on early Earth and gave rise to NTR. A phylogenetic analysis revealed six more novel-type TrxR groups and suggested that the broader flavin-containing disulfide oxidoreductase family is more diverse than previously considered. The unprecedented structural similarities between an F420-dependent enzyme (DFTR) and an NADPH-dependent enzyme (NTR) brought new thoughts to investigations on F420systems involved in microbial pathogenesis and antibiotic production.
authors: From the Department of Biochemistry.
authors: Dwi
authors: D
authors: Susanti
authors: From the Department of Biochemistry.
authors: Usha
authors: U
authors: Loganathan
authors: From the Department of Biochemistry, biswarup@vt.edu.|Biocomplexity Institute, and.|Virginia Tech Carilion School of Medicine, Virginia Tech, Blacksburg, Virginia 24061.
authors: Biswarup
authors: B
authors: Mukhopadhyay
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism*; D017013:Methanobacteriaceae / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D012256:Riboflavin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D005182:Flavin-Adenine Dinucleotide; C015084:coenzyme F420; D013880:Thioredoxin-Disulfide Reductase; D012256:Riboflavin
keywords: Methanocaldococcus jannaschii; archaea; coenzyme F420; deazaflavin; electron transfer; evolution; flavin-gated; methanogen; redox regulation; thioredoxin reductase