In a landmark development that could revolutionize the approach to plastic waste recycling, an international team of scientists has unveiled the detailed molecular workings of an enzyme capable of breaking down polyurethane, one of the most challenging and widely produced synthetic polymers. This groundbreaking study provides the first comprehensive mechanistic insight into how the esterase enzyme Aes72 cleaves urethane bonds within polyurethane (PU), a process that until now has remained elusive in the realm of biocatalytic plastic degradation.
Polyurethane, ranked as the fifth most produced synthetic polymer globally, is ubiquitous in myriad applications, ranging from foams and coatings to adhesives and elastomers. Despite its versatility and widespread use, PU presents a persistent environmental challenge due to its complex polymeric structure, which is resistant to conventional degradation methods. Mechanical and chemical recycling processes currently employed are often energy-intensive, generate toxic by-products, and require high-quality feedstocks, making sustainable processing impractical on a large scale.
Addressing these challenges, the research consortium spearheaded by experts from Nanjing Tech University, Shandong University, the Tianjin Institute of Industrial Biotechnology, and the University of Greifswald has centered its efforts on the promiscuous esterase enzyme, Aes72. Unlike many known enzymes proficient in degrading polyester-type plastics, the capacity to efficiently hydrolyze the urethane linkages in diverse polyurethane wastes had remained out of reach, impeding breakthroughs in biocatalytic recycling of PU.
Capitalizing on advanced structural biology methods, the team successfully resolved the ligand-free crystal structure of Aes72 at an exceptional resolution of 1.80 Ångströms. This high-resolution structural map illuminated the enzyme’s active site geometry and the spatial arrangement of key amino acid residues, setting the stage for a deeper understanding of the chemical steps governing polyurethane hydrolysis.
Building upon this structural foundation, the researchers employed state-of-the-art multiscale quantum mechanics/molecular mechanics (QM/MM) simulations to dissect the urethane bond cleavage mechanism at the atomic level. These simulations revealed a sophisticated four-step reaction cascade, with the nucleophilic attack on the urethane bond identified as the rate-limiting step. Understanding this catalytic bottleneck opened new avenues for targeted enzyme engineering aimed at accelerating the reaction kinetics.
Utilizing a semi-rational design approach, the scientists fine-tuned the binding pocket of Aes72 to enhance substrate accommodation and catalytic turnover. Their efforts culminated in a double mutant variant, designated F276A/L141I, which demonstrated a striking twofold increase in catalytic efficiency against the model substrate bis(4-hydroxybutyl) (methylenebis(4,1-phenylene)) dicarbamate (BMC) relative to the native enzyme. This enhancement was not limited to model substrates but translated effectively to practical PU materials.
In experimental degradation trials, the engineered Aes72 variant exhibited pronounced chain scission activity and led to significant mass reduction in thermoplastic polyether-based polyurethane samples, hallmark indicators of successful enzymatic depolymerization. These results underscore the enzyme’s potential applicability in industrial bioprocesses where environmentally benign and efficient PU recycling is imperative.
Despite these promising advances, the study also highlighted ongoing challenges posed by the structure of thermoset PU foams, which are highly cross-linked and exhibit physicochemical resistance to enzymatic degradation. These findings reassert the complexity of PU materials and the necessity for continued innovation in enzyme design to broaden the scope of biodegradable polymer substrates.
The elucidation of Aes72’s structure-function nexus establishes a crucial platform for future research into more robust and versatile biocatalysts. By integrating cutting-edge structural biology with computational enzyme engineering, this research not only advances scientific understanding but also smartly aligns with emerging circular economy models emphasizing sustainability and resource recovery.
This pioneering work signals a transformative direction for waste plastic management, shifting from conventional polluting methods toward green catalytic processes operating under mild, solvent-free conditions. By harnessing enzyme promiscuity and precision bioengineering, the scientific community edges closer to scalable and sustainable solutions for polyurethanes and other recalcitrant plastics.
The published findings, entitled “Structural Elucidation and Mechanisms-Guided Engineering of a Promiscuous Esterase for Enhanced Polyurethane Depolymerization,” represent a collaboration among Jiawei Liu, Mingna Zheng, Yuan Wen, Wei Xia, Xu Han, Jie Zhou, Weidong Liu, Ren Wei, Yanwei Li, Weiliang Dong, and Min Jiang. The article, featured in the journal Engineering, delineates the experimental and computational breakthroughs that collectively demonstrate the feasibility of enzymatic depolymerization of challenging polymers.
This study exemplifies the critical role of mechanistic insight in engineering next-generation biocatalysts, paving pathways to eco-friendly recycling technologies that can mitigate the global plastic crisis. The methodological convergence of crystallography, computational chemistry, and protein engineering serves as a blueprint for future initiatives targeting other synthetic polymers notorious for environmental persistence.
The implications of this research extend beyond academic novelty; industrial sectors reliant on plastic materials stand to benefit significantly from enzymatic tools that promise reduced energy footprints and minimized toxic by-product formation. The tailored Aes72 enzyme variant embodies a tangible step forward in transforming PU waste streams into recyclable feedstocks, heralding a sustainable leap toward closed-loop plastics economies.
The work represents a profound synthesis of molecular understanding and applied biotechnology, offering hope that rational enzyme redesign can ultimately surmount the long-standing barriers to effective plastic recycling. As the global demand for sustainable materials intensifies, innovations like this catalytic breakthrough provide critical momentum for environmental stewardship and economic viability in plastics management.
Subject of Research: Enzymatic degradation of polyurethane via engineered esterase Aes72
Article Title: Structural Elucidation and Mechanisms-Guided Engineering of a Promiscuous Esterase for Enhanced Polyurethane Depolymerization
News Publication Date: 14 February 2026
Web References: https://doi.org/10.1016/j.eng.2026.02.008, https://www.sciencedirect.com/journal/engineering
References: Liu et al., Engineering, 2026
Image Credits: Jiawei Liu et al.
Keywords: polyurethane degradation, esterase Aes72, enzyme engineering, biocatalytic recycling, polyurethane hydrolysis, polyurethane waste management, quantum mechanics/molecular mechanics simulations, protein engineering, polymer depolymerization, sustainable plastics, plastic enzymatic recycling, circular economy
