Unveiling Mechanistic and Structural Insights of EstS1 Esterase: A Potent Broad-Spectrum Phthalate Diester Degrading Enzyme

The ubiquitous presence of plastics and plasticizers around the globe has raised an alarming condition. Phthalate diesters are high-priority pollutants that mimic natural hormones and act as endocrine disruptors upon entering living systems. While certain bacterial esterases have been identified for their role in phthalate diester degradation, their structural and mechanistic characteristics remain largely unexplored. A thermostable and pH-tolerant EstS1 esterase from Sulfobacillus acidophilus catalyzes the conversion of low molecular weight phthalate diesters to monoesters. This study highlights the unique potential of EstS1 to degrade high molecular weight bis(2-ethylhexyl) phthalate (DEHP) by employing biophysical and biochemical approaches along with in-depth structural analysis utilizing high-resolution crystal structures in both apo and complex forms, with various substrates, products, and their analogs to elucidate mechanistic details. The catalytic tunnel mediating entry and exit of the substrate and product, respectively, centralized the Ser-His-Asp triad performing catalysis by bi-bi ping-pong mechanism, forming a tetrahedral intermediate. Additionally, structural analysis of the polypropylene analog jeffamine with EstS1 revealed effective covalent binding, demonstrating its multifunctional capability. Mutation analysis showed that the Met207Ala mutation abolished DEHP binding at the active site, confirming its essential role in supporting catalysis. These findings underscore the potential of EstS1 as a key tool for advancing technologies aimed at phthalate diesters biodegradation.