Metabolic pathways of aerobic bacteria able to assimilate sulfur can provide biocatalysts for biodesulfurization of petroleum and of other sulfur-containing pollutants. Of major interest is the so-called "4S pathway," in that C-S bonds are specifically cleaved leaving the carbon skeleton of substrates intact. This pathway is carried out by four enzymes, named Dsz A, B, C, and D. In view of a possible application of recombinant Dsz enzymes in biodesulfurization treatments, we have investigated the structural features of enzymes cloned from a Rhodococcus strain isolated from polluted environmental samples and their resistance to temperature (20-95 °C) and to organic solvents (5, 10, and 20 % v/v methanol, acetonitrile, hexane, and toluene). Changes in protein structures were assessed by circular dichroism and intrinsic fluorescence spectroscopy. We found that all Dsz proteins are unfolded by temperatures in the range 45-60 °C and by all solvents tested, with the most dramatic effect being produced by toluene. These results suggest that stabilization of the biocatalysts by protein engineering will be necessary for developing biodesulfurization technologies based on Dsz enzymes.
Keywords: Biodesulfurization; Dsz pathway enzymes; Enzymes stability; Organic solvents.