Emerging trends on the role of recombinant pectinolytic enzymes in industries- an overview

Fungal pectinases: an insight into production, innovations and applications

The fungal system holds morphological plasticity and metabolic versatility which makes it unique. Fungal habitat ranges from the Arctic region to the fertile mainland, including tropical rainforests, and temperate deserts. They possess a wide range of lifestyles behaving as saprophytic, parasitic, opportunistic, and obligate symbionts. These eukaryotic microbes can survive any living condition and adapt to behave as extremophiles, mesophiles, thermophiles, or even psychrophile organisms. This behaviour has been exploited to yield microbial enzymes which can survive in extreme environments. The cost-effective production, stable catalytic behaviour and ease of genetic manipulation make them prominent sources of several industrially important enzymes. Pectinases are a class of pectin-degrading enzymes that show different mechanisms and substrate specificities to release end products. The pectinase family of enzymes is produced by microbial sources such as bacteria, fungi, actinomycetes, plants, and animals. Fungal pectinases having high specificity for natural sources and higher stabilities and catalytic activities make them promising green catalysts for industrial applications. Pectinases from different microbial sources have been investigated for their industrial applications. However, their relevance in the food and textile industries is remarkable and has been extensively studied. The focus of this review is to provide comprehensive information on the current findings on fungal pectinases targeting diverse sources of fungal strains, their production by fermentation techniques, and a summary of purification strategies. Studies on pectinases regarding innovations comprising bioreactor-based production, immobilization of pectinases, in silico and expression studies, directed evolution, and omics-driven approaches specifically by fungal microbiota have been summarized.

Flow-cytometric cell sorting coupled with UV mutagenesis for improving pectin lyase expression

Introduction: Alkaline pectin lyase is an important enzyme with a wide range of applications in industrial production, It has been widely used in many important fields such as fruit juice processing and extraction, the dyeing and processing of cotton and linen textiles, degumming plant fibers, environmental industrial wastewater treatment, and pulp and paper production. PGLA-rep4 was previously generated as a modified alkaline pectin lyase with high specific activity at pH 11.0°C and 70°C. However, the pre-constructed high-activity pectin lyase expression strains are still difficult to apply in industrial production due to their limited enzymatic activity. We hope to solve these problems by combining modern breeding techniques with high-throughput equipment to rapidly screen alkaline pectin lyase with higher enzymatic activity and lower cost. Methods: We fused the genes encoding PGLA-rep4 and fluorescent protein egfp using a flexible linker peptide and ligated them into a temperature-sensitive plasmid, pKD46. The constructed screening plasmid pKD46-PGLA-rep4-egfp was then transformed into an expression host and screened via flow-cytometric cell sorting coupled with UV mutagenesis. Results: Following mutagenesis, primary screening, and secondary screening, the high-expression strain, named Escherichia coli BL21/1G3, was obtained. The screening plasmid pKD46-PGLA-rep4-egfp was eliminated, and the original expression plasmid pET28a-PGLA-rep4 was then retransformed into the mutant strains. After induction and fermentation, pectin lyase activity in E. coli BL21/1G3 was significantly increased (1.37-fold relative to that in the parental E. coli BL21/PGLA-rep4 strain, p < 0.001), and the highest activity was 230, 240 U/mL at 144 h. Genome sequencing revealed that genes encoding ribonuclease E (RNase E) and diadenosine tetraphosphatase (ApaH) of E. coli BL21/1G3 were mutated compared to the sequence in the original E. coli BL21 (DE3) strain, which could be associated with increased enzyme expression. Discussion: Our work provides an effective method for the construction of strains expressing pectin lyase at high levels.

Elucidating structure of pectin in ramie fiber to customize enzyme cocktail for high-efficiency enzymatic degumming

Pectin is one of the main components of bast fiber including ramie fiber, and must be removed before use. Enzymatic degumming is the preferred process as it is an environment-friendly, simple and controllable process for ramie degumming. However, an important problem limiting wide application of this process is the high cost due to the low efficiency of enzymatic degumming. In this study, pectin samples were extracted from raw ramie fiber and degummed ramie fiber, respectively, and their structures were characterized and compared to allow tailoring of an enzyme cocktail for degrading the pectin. It was elucidated that pectin from ramie fiber is composed of low esterified homogalacturonan (HG) and low branched rhamnogalacturonan I (RG-I), and the ratio of HG/RG-I is 1.72:1. Based on the pectin structure, potential enzymes to be used for enzymatic degumming of ramie fiber were proposed and an enzyme cocktail was customized. Degumming experiments confirmed that the customized enzyme cocktail can effectively remove pectin from ramie fiber. To our knowledge, this is the first time the structural characteristics of pectin in ramie fiber have been clarified, and it also provides an example of tailoring a specific enzyme system to achieve high-efficiency degumming for biomass containing pectin.

Improvement of optimum pH and specific activity of pectate lyase from Bacillus RN.1 using loop replacement

Background: Alkaline pectate lyase plays an important role in papermaking, biological refining and wastewater treatment, but its industrial applications are largely limited owing to its low activity and poor alkali resistance. Methods: The alkaline pectate lyase BspPel from Bacillus RN.1 was heterologously expressed in Escherichia coli BL21 (DE3) and its activity and alkali resistance were improved by loop replacement. Simultaneously, the effect of R260 on enzyme alkaline tolerance was also explored. Results: Recombinant pectate lyase (BspPel-th) showed the highest activity at 60°C and pH 11.0, and showed significant stability over a wide pH range (3.0-11.0). The specific enzyme activity after purification was 139.4 U/mg, which was 4.4 times higher than that of the wild-type enzyme. BspPel-th has good affinity for apple pectin, since the V _max and K _m were 29 μmol/min. mL and 0.46 mol/L, respectively. Molecular dynamics simulation results showed that the flexibility of the loop region of BspPel-th was improved. Conclusion: The modified BspPel-th has considerable potential for industrial applications with high pH processes.

A thermotolerant and pH stable rhamnogalacturonan acetylesterase (CtPae12B), a family 12 carbohydrate esterase from Clostridium thermocellum with broad substrate specificity

The gene encoding rhamnogalacturonan acetylesterase, CtPae12B from Clostridium thermocellum was cloned, expressed, purified and biochemically characterized. Purified CtPae12B was soluble and exhibited homogenous single band. Phylogenetically it was most closely related to an RGAE, YesT from B. subtilis. CtPae12B production was maximum with LB medium. CtPae12B showed optimal temperature, 65 °C and thermostability with half-life, 5.1 h at 80 °C. CtPae12B was alkaliphilic with optimal pH, 8.0, while it displayed stability at both acidic and alkaline pH ranges. Inhibition of CtPae12B activity by PMSF showed the importance of nucleophilic serine in the catalytic triad. The metal ions, chemical or chelating agents used, did not enhance CtPae12B activity, which was also corroborated by protein melting study. The enzymatic activity of CtPae12B remained unaffected by 5 M urea. CtPae12B showed broad substrate specificity as it displayed activity against a range of synthetic substrates showing highest V_max, 770 U/mg and K_m, 1.2 mM with β-D-gluco pentaacetate. CtPae12B could deacetylate both pectic and xylan substrates showing highest V_max, 770 U/mg and K_m, 13.4 mg/mL with potato rhamnogalacturonan and V_max, 105 U/mg and K_m, 7.1 mg/mL with acetylated birchwood xylan. The thermostability, pH stability and broad substrate specificity of CtPae12B makes it a versatile enzyme for industrial applications.