Pectin, a heteropolysaccharide derived from plant cell walls, is essential in the food, pharmaceutical, and environmental industries. Currently, citrus and apple peels are the primary sources for commercial pectin production. The yield and quality of pectin extracted from various plant sources significantly differ based on the extraction methods employed, which include physical, chemical, and biological processes. The complex structures of pectin, composed of polygalacturonic acid and rhamnogalacturonan, influence its physicochemical properties and, consequently, its functionality. As a common polysaccharide, pectin finds applications across multiple sectors. In the food industry, it acts as a gelling agent and a packaging material; in pharmaceuticals, it is utilized for drug delivery and wound healing. Environmentally, pectin contributes to wastewater treatment by adsorbing pollutants. Current research focuses on alternative sources, sustainable extraction methods, and multifunctional applications of pectin. Ongoing studies aim to enhance extraction technologies and broaden the applications of pectin, thereby supporting sustainable development goals.

To improve the thermal stability of pectate lyase for ramie degumming, we modified the novel pectate lyase gene (pelG403) derived from the Dickeya dadantii DCE-01 high-efficiency ramie degumming strain by site-directed mutagenesis. Twelve mutants were acquired, wherein a prospective mutant (A129V) showed better enzyme activity and thermal stability. Compared with the wild type (PelG403), the specific enzyme activity and the optimal reaction temperature of A129V in the fermentation broth increased by 20.1%, and 5 °C, respectively. Under the conditions of 55 °C and pH 9.0, the weightlessness rate of ramie raw materials of A129V increased by 6.26%. Therefore, this study successfully improved the enzyme activity and heat resistance of PelG403 in an alkaline environment, which may contribute to the development of enzyme preparations and the elucidation of the mechanism for ramie bio-degumming.

In order to obtain a thermostable pectate lyase for ramie degumming, a rational design based on structural analysis was carried out on a novel pectate lyase (Pel419) derived from the Dickeya Dadantii DCE-01 for high-efficiency ramie degumming. A total of five potential amino acid sites were chosen to replace residues. Then, the mutant enzymes were subjected to the heterologous expressions in Escherichia coli and their enzymatic characteristics were determined. The optimal reaction temperature for the five mutants kept consistent with that for the wild type. The enzyme activity and thermal stability of mutant V52A were significantly improved. Meanwhile, the weight loss rate obtained by V52A with the best enzymatic characteristics in the ramie degumming process at 50 °C is comparable with that obtained by commercial cotton-ramie processing pectinases, indicating that V52A was a potential industrial enzyme that could be applied to large-scale ramie degumming. In this study, the biological functions of conservative residues of Pel419 were preliminarily explored. The mutant V52A with both enzymatic activity and improved heat resistance was acquired, providing a superior material for developing enzyme preparations of ramie degumming, and rendering an effective method for the rational design aiming to improve the thermostability of pectate lyase.

Xylanase, an essential enzyme for breaking down xylan, faces limitations in its industrial applications due to the relatively low catalytic activity of the wild type. Directed evolution was used to enhance the catalytic efficiency of xylanase that originated from the Dickeya dadantii DCE-01. A xylanase variant (Xyn-ep) was obtained with improved catalytic activity by random mutant library employing two rounds of error-prone PCR. The results showed that the Xyn-ep demonstrated enzyme activity 1.6 times higher than that of wild-type xylanase. Sequencing analysis pinpointed key mutation sites at S159P, K212N, and N397S, respectively. Homology modeling was used to analyze the location of the mutation sites and to investigate the mechanism of the improved catalytic performance. The mutant Xyn-ep showed improved catalytic performance by error-prone PCR. Additionally, the increased flexibility of the loop of the mutant may contribute to the enhanced activity. These findings indicate that error-prone PCR is an effective method for enhancing enzyme activity and that the mutant Xyn-ep may be a new GH30 xylanase, being a potential candidate for industrial applications such as bast fiber bio-degumming, cotton bio-refinery, paper making, and so on.

Lipase, a type of enzyme that decomposes and synthesizes triglycerides, plays an important role in lipid processing. In this study, a heat-resisting lipase gene (lip4) from Thermomyces lanuginosus was subcloned into the pPICZαA vector and then transformed into Pichia pastoris X33. The recombinant yeast cell concentration reached the maximum (119.5 g/L) at 144 h, and the lipase (Lip4) activity reached the maximum (3900 U/mL) at 168 h in 10 L bioreactor. Through bioinformatics analysis, S168, as the key site of Lip4, participated in the formation of the catalytic triads S168-D223-H280 and G166-H167-S168-L169-G170. Furthermore, S168 and seven conserved amino acids of G104/288, S105, A195, P196, V225 and I287 constitute the active center of Lip4. Specifically, the structure modeling showed two α-helices of the lid domain, outside the active pocket domain, controlling the entry of the substrate on Lip4. The potential glycosylation of Asn-33 may be involved in exhibiting the high stable temperature for lipase activity. Therefore, the eukaryotic system was constructed to express Lip4 efficiently, and the amino acid sites related to the catalytic efficiency of Lip4 were clarified, providing a new way for its subsequent property research and industrial application.

Microbial degumming offers an environmentally sustainable route for the extraction of natural ramie fibers. However, there are currently no genetically engineered bacteria suitable for large-scale industrial production. In this study, Dickeya dadantii strain DCE-01, a dominant ramie-degumming bacterium, was systematically investigated using time-resolved quantitative proteomics. This research revealed a temporally coordinated, multi-enzyme catalytic mechanism, in which pectate lyases were highly expressed at the initial stage to rapidly depolymerize surface pectin, followed by sustained expression of hemicellulases that ensured the complete removal of residual non-cellulosic materials. Quantitative real-time PCR (qRT–PCR) results showed strong concordance with the proteomic data, confirming that transcriptional regulation drives the dynamic enzymatic response. This integrative analysis, linking macroscopic morphological evolution with microscopic molecular changes, elucidates the intrinsic mechanism underlying efficient biological degumming by D. dadantii strain DCE-01 and provides valuable insights for the rational design of high-performance engineered bacteria for industrial fiber processing.