Molecular cloning, sequencing and characterization of cDNA to rat liver rhodanese, a thiosulphate sulphurtransferase

Rhodanese (EC 2.8.1.1), a mitochondrial thiosulphate sulphurtransferase, is involved in the formation of iron-sulphur complexes and cyanide detoxification. By screening a rat liver cDNA library with oligonucleotide probes complementary to portions of the published bovine rhodanese peptide sequence, rat rhodanese cDNA clones were obtained and sequenced. Comparison of the rat rhodanese cDNA open reading frame with the bovine peptide sequence demonstrated in the rat open reading frame the presence of 27 amino acid substitutions, only five of which are highly non-conservative. Thus the rat enzyme is approx. 91% identical with bovine rhodanese, or about 98% similar when conservative substitutions are considered. In addition, the rat translation product contains a Gly-Lys-Ala C-terminal tripeptide that was not observed in the bovine peptide sequence. All cysteine and proline residues are invariant between the two mammalian proteins. Computer-generated structural modelling of rat rhodanese indicated that few amino acid substitutions were present within close proximity to the active site or within the hinge region (connecting loop) between the A and B domains. Furthermore, evidence is presented showing that rhodanese is highly conserved at the DNA level among rodents, primates and a variety of other vertebrates.