Gene cloning and characterization of a psychrophilic phthalate esterase with organic solvent tolerance from an Arctic bacterium Sphingomonas glacialis PAMC 26605

Abstract

Phthalate esters (PEs) are commonly used as plasticizers to soften household and industrial plastic products. The wide use of PEs has become a public health concern as they are considered toxic to human health and PE contamination of the environment is increasing. In this study, we cloned a gene encoding the psychrophilic phthalate esterase (hereafter referred to as EstSP1) from an Arctic bacterium, Sphingomonas glacialis PAMC 26605, and characterized the properties of recombinant EstSP1 protein. EstSP1 belongs to the α/β hydrolase family and its catalytic triad consists of Ser 161, Asp 253, and His 283 residues. Thermal stability and protein folding of EstSP1 were reduced under ambient temperatures when compared with those at 4°C, despite EstSP1 maintaining its secondary structure at 4°C–50°C. EstSP1 is unique among cold-adapted esterases in that it not only has substrate preferences for phthalates with shorter ester chains (C2–C6), but also tolerance to polar organic solvents, including alcohols and DMSO. Furthermore, EstSP1 exhibited a larger change in conformational flexibility in ethanol, isopropanol, and DMSO when evaluated by acrylamide-induced fluorescence quenching. The results indicate that EstSP1 is a novel organic solvent-tolerant, psychrophilic phthalate esterase.