Identification of a TeO32− reductase/mycothione reductase fromRhodococcus erythropolisPR4

Abstract

ABSTRACTA Rhodococcus erythropolis bacterium that tolerates normally lethal concentrations of Fe(II), Cu(II), AsO32−, SeO32−, TeO32−, Cd(II) and Zn(II) was identified from an environmental isolate. In characterizing the molecular basis for metal tolerance, a mycothione reductase (Mtr) with remarkable selectivity for TeO32− reduction over SeO32− was identified. In equimolar concentrations of TeO32− and SeO32−, the enzymatic product contains a 7-fold excess of Te. This selectivity is remarkable because the standard reduction potential of SeO32− is 0.20 V more favorable for reduction than TeO32. Selectivity of the enzyme for TeO32− decreases with increasing assay pH. Homology modeling of the enzyme identifies four aromatic residues near the active site, including two histidine residues, that are not present in a related SeO32− preferring reductase. On the basis of more favorable π-interactions for Te than for Se and the pH dependence of the selectivity, the Te-selectivity is attributed in part to these aromatic residues. The resulting Te0 enzymatic product resembles Te nanowires.