Phthalic acid esters (PAEs) are widely used as plastic additives to increase the flexibility and durability of plastics. Constantly leaching out from plastics, PAEs are ubiquitously found in the environment. As PAEs exhibit biological activities such as being endocrine disruptive, the quest for efficient degradation strategies continues. Here, we report a bienzymatic degradation system for PAEs to phthalic acid (PA) using a cascade comprising two hydrolases, EstJ6 and P8219. The reaction conditions were optimized with respect to concentrations of both enzymes, temperature, and initial pH. Finally, the substrate scope of the new cascade was investigated, revealing that particularly PAEs with relatively small alcohols were degraded to more than 90 %. This present study provides a potential doable biocatalytic strategy for the complete hydrolysis of PAEs.
Phthalate acid esters (PAEs), a group of xenobiotic compounds used extensively as plasticizers, have attracted increasing concern for adverse effects to human health and the environment. Microbial degradation relying on PAE hydrolases is a promising treatment. However, only a limited number of PAE hydrolases were characterized to date. Here we report the structures of MehpH, a monoalkyl phthalate (MBP) hydrolase that catalyzes the reaction of MBP to phthalic acid and the corresponding alcohol, in apo and ligand-bound form. The structures reveal a positively-charged catalytic center, complementary to the negatively-charged carboxyl group on MBP, and a penetrating tunnel that serves as exit of alcohol. The study provides a first glimpse into the enzyme-substrate binding model for PAE hydrolases, leading strong support to the development of better enzymes in the future.
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