A thioredoxin reductase-like protein from the thermophile, Thermus scotoductus SA-01, displaying iron reductase activity

The transition metal iron is an important element for the sustenance of life - it can function either as an electron acceptor or as a donor and serves as a cofactor in many enzymes activities. The cytoplasmic NAD(P)H-dependent ferric reductase in Thermus scotoductus SA-01 shares high sequence and structural similarity to prokaryotic thioredoxin reductases. Here we report the sequence of the ferric reductase (which is typically annotated as a thioredoxin reductase-like protein) and a comparative kinetic study with the thioredoxin reductase from SA-01. Structurally, the most noteworthy difference, immediately apparent from the protein sequence, is the absence of the disulphide redox centre in the ferric reductase. This is the first report relating the attributes of such a redox protein to its ability to reduce a ferric substrate.