Pyridine nucleotide-disulphide oxidoreductases class-II active site

The pyridine nucleotide-disulphide oxidoreductases are FAD flavoproteins which contains a pair of redox-active cysteines involved in the transfer of reducing equivalents from the FAD cofactor to the substrate. On the basis of sequence and structural similarities [1] these enzymes can be classified into two categories. The second category groups together the following enzymes:

• Bacterial and fungal thioredoxin reductase (EC 1.8.1.9) (gene trxB) [2].
• Salmonella typhimurium alkyl hydroperoxide reductase protein F52a (gene aphF) [3], an enzyme that serves to protect the cell against damage to DNA by alkyl hydroperoxides.
• NADH dehydrogenase (EC 1.6.99.3) from Bacillus strain YN-1 (gene ndh) [4].
• A probable oxidoreductase which is encoded in the Clostridium pasteurianum rubredoxin operon [5].
• Yeast hypothetical protein YHR106w.

The sequence around the two cysteines involved in the redox-active disulfide bond is conserved and can be used as a signature pattern.