Highly Stable Thermophilic Dehalogenase from Sulfolobus Tokodaii for Dechlorination of Organic Pollutants

Sulfolobus tokodaii is a thermophilic aerobic archeaon that is found in hot springs in Japan. Since thermophiles live in very harsh conditions, their proteins have to be very stable in order to function properly. Based on homology, a gene was identified from this organism that putatively expresses a dehalogenase enzyme. The putative dehalogenase was cloned and expressed in E. coli. It was found that the recombinant protein can dechlorinate 2-chloropropionic acid but not haloalkanes. The enzyme acts stereospecifically on the L-form of the substrate, with K_m and v_max values of 1.7 mM and 0.35 μmol/min, respectively. The optimal temperature in terms of activity for the dehalogenase is between 70 and 80 ^oC. While the optimum catalytic activity of this thermophilic dehalogenase is comparable to other L-2-haloacid dehalogenases from mesophiles, the stability is drastically improved. The recombinant dehalogenase remains fully active after four hours of incubation at 70 ^oC, and tolerates prolonged incubation at pH ranging from 4 to 10. Furthermore, the enzyme can be purified conveniently by a two-step, heat-plus-acid treatment. The high expression yield and easy purification procedure make the recombinant dehalogenase an ideal candidate for biotechnology applications, i.e., dechlorination of halogenated organic pollutants in environmental clean-up.