Structural and mechanism-based engineering of sulfotransferase CHST15 for the efficient synthesis of chondroitin sulfate E

Natural chondroitin sulfate (CS), extracted from animal cartilage, is widely used in the pharmaceuticals and foods. However, contamination with animal-derived heteropolysaccharides presents significant challenges, including potential immune responses. To address this, we developed a green and efficient method for synthesizing chondroitin sulfate E (CSE) via enzymatic synthesis, identifying EcCHST15, a sulfotransferase that catalyzes the conversion of chondroitin sulfate A (CSA) to CSE. We investigated the novel catalytic mechanism of CHST15 through quantum mechanical (QM) calculations and experimental validation, confirming its alignment with the SN2 reaction mechanism. Subsequently, we enhanced the catalytic efficiency of CHST15 using protein engineering, improving the catalytic efficiency from 18.1% in the wild type (WT) to 62.5% in the M7 mutant—a 3.5-fold increase. Finally, we constructed a six-enzyme cascade whole-cell catalyst, achieving a 72.2% conversion of 15 g/L CSA to produce CSE within 24 h. These findings offer a promising strategy for the industrial production of CSE.