Phthalic acid esters (PAEs), which are widespread environmental contaminants, can be efficiently biodegraded, mediated by enzymes such as hydrolases. Despite great advances in the characterization of PAE hydrolases, which are the most important enzymes in the process of PAE degradation, their molecular catalytic mechanism has rarely been systematically investigated. Acinetobacter sp. LUNF3, which was isolated from contaminated soil in this study, demonstrated excellent PAE degradation at 30 °C and pH 5.0-11.0. After sequencing and annotating the complete genome, the gene dphAN1, encoding a novel putative PAE hydrolase, was identified with the conserved motifs catalytic triad (Ser201-Asp295-His325) and oxyanion hole (H127GGG130). DphAN1 can hydrolyze DEP (diethyl phthalate), DBP (dibutyl phthalate) and BBP (benzyl butyl phthalate). The high activity of DphAN1 was observed under a wide range of temperature (10-40 °C) and pH (6.0-9.0). Moreover, the metal ions (Fe2+, Mn2+, Cr2+ and Fe3+) and surfactant TritonX-100 significantly activated DphAN1, indicating a high adaptability and tolerance of DphAN1 to these chemicals. Molecular docking revealed the catalytic triad, oxyanion hole and other residues involved in binding DBP. The mutation of these residues reduced the activity of DphAN1, confirming their interaction with DBP. These results shed light on the catalytic mechanism of DphAN1 and may contribute to protein structural modification to improve catalytic efficiency in environment remediation.
Keywords: Acinetobacter; HSL family hydrolase; biodegradation; genome sequencing; site-directed mutagenesis.