Heterologous Expression and Characterization of a Novel Polygalacturonase (DdpgA) from Dickeya dadantii DCE-01 and Its Application in Bioscouring of Ramie Fabric

Efficient and eco-friendly bioscouring of ramie fabric is a critical step in the textile industry. To obtain polygalacturonase (DdpgA) suitable for the bioscouring of ramie fabric, a novel polygalacturonase gene (ddpgA) from the ramie-biodegumming strain Dickeya dadantii DCE-01 was subjected to bioinformatic analysis and heterologous expression. The recombinant plasmid pET28a-ddpgA was introduced into E. coli BL21(DE3), and the engineering strain BL21/pET28a-ddpgA was constructed; then induction conditions were optimized by response surface methodology. The recombinant DdpgA was purified and enzymatically characterized and further applied to the treatment of greige ramie fabric in combination with mannanase and xylanase. The results showed that the optimal pH of DdpgA was 5.0 and the optimal temperature was 55 °C; the enzyme was stable over the pH range of 3.0–6.0 and retained more than 50% of its activity after incubation at 55 °C for 60 min. DdpgA exhibited the highest catalytic activity toward sodium polygalacturonate. Mn²⁺ significantly activated DdpgA, whereas Ba²⁺, Pb²⁺, and Cu²⁺ inhibited its activity. Compound-enzyme scouring of ramie fabric formulated with DdpgA achieved a weight loss rate of 15.22%, a pectin removal rate of 51.28%, and a water-drop wetting time of less than 2 s; scanning electron microscopy confirmed the effective removal of gummy composites from the ramie fiber surface. This enzymatic scouring for ramie fabric avoids the strong alkali and high temperature required by conventional alkalic scouring, and thus represents an environmentally friendly alternative for ramie-fiber processing. Therefore, this study achieved high-level soluble expression of ddpgA in E. coli and obtained an acidic mesophilic polygalacturonase with demonstrated ramie bioscouring performance.