Identification and characterization of a meta-cleavage product hydrolase involved in biphenyl degradation from Arthrobacter sp. YC-RL1.

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants (POPs) widely existing in the environment. Arthrobacter sp. YC-RL1 is a biphenyl-degrading bacterium that shows metabolic versatility towards aromatic compounds. A 2-hydroxy-6-oxo-6-phenylhexa-2, 4-dienoate (HOPDA) hydrolase (BphD) gene involved in the biodegradation of biphenyl was cloned from strain YC-RL1 and heterologously expressed in Escherichia coli BL21 (DE3). The recombinant BphD was purified and characterized. BphD showed the highest activity at 45 °C and pH 7. It was stable under a wide range of temperature (20-50 °C). The enzyme had a K value of 0.14 mM, K of 11.61 s, and V of 0.027 U/mg. Temperature dependence catalysis exhibited a biphasic Arrhenius Plot with a transition at 20 °C. BphD was inactivated by SDS, Tween 20, Tween 80, Trition X-100, DTT, CHAPS, NBS, PMSF, and DEPC, but insensitive to EDTA. Site-directed mutagenesis of the active-site residues revealed that the catalytic triad residues (Ser115, His275, and Asp247) of BphD were necessary for its activity. The investigation of BphD not only provides new potential enzyme resource for the biodegradation of biphenyl but also helps deepen our understanding on the catalytic process and mechanism.