A new subfamily of agmatinases present in methanogenic Archaea is Fe(II) dependent

Here we report that the Methanocaldococcus jannaschii enzyme derived from the MJ0309 gene is an Fe(II) dependent agmatinase (SpeB). This is the first report of an iron-dependent agmatinase. We demonstrate that aerobically isolated recombinant enzyme contains two disulfide bonds and only a trace amount of any metal and requires the presence of both dithiothreitol (DTT) and 4 equiv of Fe(II) for maximum activity. The DTT activation could be indicative of the presence of a redox system, which would regulate the activity of this as well as other enzymes in the methanogens. Site-directed mutagenesis of the four conserved cysteines C71, C136, C151, and C229 to alanine or serine showed that only the C71 and C151 mutants showed a significant drop in activity indicating that the disulfide bond responsible for regulating activity was likely between C136 and C229. We propose that the C71 and C151 cysteine thiols, produced by the DTT-dependent reduction of their disulfide, are two additional metal binding ligands that alter the metal specificity of the M. jannaschii agmatinase from Mn(II) to Fe(II).