Efficient expression of an alkaline pectate lyase gene from Bacillus subtilis and the characterization of the recombinant protein

Critical Factors for Optimum Biodegradation of Bast Fiber’s Gums in Bacterial Retting

Bast fiber plants require a post-harvest process to yield useable natural cellulosic fibers, denoted as retting or degumming. It encompasses the degradation of the cell wall’s non-cellulosic gummy substances (NCGs), facilitating fibers separations, setting the fiber’s quality, and determining downstream usages. Due to the inconvenience of traditional retting practices, bacterial inoculum and enzyme applications for retting gained attention. Therefore, concurrent changes of agroclimatic and socioeconomic conditions, the conventional water retting confront multiple difficulties, bast industries become vulnerable, and bacterial agents mediated augmented bio-retting processes trying to adapt to sustainability. However, this process’s success demands a delicate balance among substrates and retting-related biotic and abiotic factors. These critical factors were coupled to degrade bast fibers NCGs in bacterial retting while holistically disregarded in basic research. In this study, a set of factors were defined that critically regulates the process and requires to be comprehended to achieve optimum retting without failure. This review presents the bacterial strain characteristics, enzyme potentials, specific bast plant cell wall’s structure, compositions, solvents, and interactions relating to the maximum NCGs removal. Among plants, associated factors pectin is the primary biding material that determines the process’s dynamics, while its degree of esterification has a proficient effect through bacterial enzymatic degradation. The accomplished bast plant cell wall’s structure, macerating solvents pH, and temperature greatly influence the bacterial retting process. This article also highlights the remediation process of water retting pollution in a biocompatible manner concerning the bast fiber industry’s endurance.

Origins and features of pectate lyases and their applications in industry

Pectate lyase treatment can be an alternative strategy of the chemical processing, which causes severe environmental pollution, and has been broadly studied and applied for diverse industrial applications including textile industry, beverage industry, pulp processing, pectic wastewater pretreatment, and oil extraction. This review gave a brief description of the origins, enzymatic characterizations, structure, and applications of pectate lyases (Pels). Most of the reported pectate lyases are originated from microorganisms with a small number of them from plants and animals. Due to the diverse environments that these microorganisms exist, Pels present diversified features, especially for the range of optimal pH and temperature. The diversified biochemical properties of Pels define their applications in different industries, and the applications of alkaline Pels on cotton bioscouring and ramie degumming in textile industry were focused in this review. This review also discussed the perspectives of the development and applications of Pels. KEY POINTS: • The first review on pectate lyase focusing on biotechnological applications. • Origins, features, structures, applications of pectate lyases reviewed. • Applications of alkaline Pels in textile industry demonstrated. • Perspectives on future development and applications of Pels discussed.

Biochemical characterization and evolutionary analysis of a novel pectate lyase from Aspergillus parasiticus

In this study, a novel pectate lyase (ApPel1) was identified and characterized from Aspergillus parasiticus. The ApPel1 hydrolysed oligogalacturonides (OGs) effectively and produced 4,5-unsaturated OGs from low-methoxyl (LM) pectin, with DP 2 to DP 5 as the major products. Furthermore, the multiple sequence alignments, structure model and phylogenetic analyses of the ApPel1 indicated that its catalytic active sites were highly conserved with other pectin lyases (PLs) and the Ca²⁺ binding amino acid residues are different compared with pectate lyases (Pels). N187D, N191D and N187D/N191D mutants were constructed to test for both Ca²⁺ binding properties and the effects on catalytic ability. The three mutations sharply decreased the activity of ApPel1 and Ca²⁺ tolerance, indicating that the Ca²⁺ binding amino acid residues are different from the other Pels. Based on the sequence and structure comparison between PLs and Pels, and mutation analysis, the ApPel1 may be direct evolution from PLs. Thus, this enzyme has potential for use in producing unsaturated OGs for biological activity study, and contributes to an improved understanding of the evolutionary relationships between PLs and Pels.

A Novel PL9 Pectate Lyase from Paenibacillus polymyxa KF-1: Cloning, Expression, and Its Application in Pectin Degradation

Pectate lyases play an important role in pectin degradation, and therefore are highly useful in the food and textile industries. Here, we report on the cloning of an alkaline pectate lyase gene (pppel9a) from Paenibacillus polymyxa KF-1. The full-length gene (1350 bp) encodes for a 449-residue protein that belongs to the polysaccharide lyase family 9 (PL9). Recombinant PpPel9a produced in Escherichia coli was purified to electrophoretic homogeneity in a single step using Ni2+-NTA affinity chromatography. The enzyme activity of PpPel9a (apparent molecular weight of 45.3 kDa) was found to be optimal at pH 10.0 and 40 °C, with substrate preference for homogalacturonan type (HG) pectins vis-à-vis rhamnogalacturonan-I (RG-I) type pectins. Using HG-type pectins as substrate, PpPel9a showed greater activity with de-esterified HGs. In addition, PpPel9a was active against water-soluble pectins isolated from different plants. Using this lyase, we degraded citrus pectin, purified fractions using Diethylaminoethyl (DEAE)-sepharose column chromatography, and characterized the main fraction MCP-0.3. High-performance gel permeation chromatography (HPGPC) analysis showed that the molecular mass of citrus pectin (~230.2 kDa) was reduced to ~24 kDa upon degradation. Ultra-performance liquid chromatography - tandem mass spectrometer (UPLC-MS) and monosaccharide composition analyses demonstrated that PpPel9a worked as an endo-pectate lyase, which acted primarily on the HG domain of citrus pectin. In vitro testing showed that the degradation product MCP-0.3 significantly promotes the growth of Lactobacillus plantarum and L. rhamnosus. In this regard, the enzyme has potential in the preparation of pharmacologically active pectin products.

Industrially produced pullulanases with thermostability: Discovery, engineering, and heterologous expression

Pullulanases (EC 3.2.1.41) are well-known starch-debranching enzymes widely used to hydrolyze α-1,6-glucosidic linkages in starch, pullulan, amylopectin, and other oligosaccharides, with application potentials in food, brewing, and pharmaceutical industries. Although extensive studies are done to discover and express pullulanases, only few are available with desirable characteristics for industrial applications. This raises the challenge to mine new enzyme sources, engineer proteins based on sequence/structure, and regulate expressions. We review here the identification of extremophilic and mesophilic microbes as sources of industrial pullulanases with desirable characteristics, including acid-resistance, thermostability, and psychrotrophism. We present current advances in site-directed mutagenesis and sequence/structure-guided protein engineering of pullulanases. In addition, we discuss heterologous expression of pullulanases in prokaryotic and eukaryotic microbial systems, and address the effectiveness of the expression elements and their regulation of enzyme production. Finally, we indicate future research needs to develop desired industrial pullulanases.

Screening of a Novel Polysaccharide Lyase Family 10 Pectate Lyase from Paenibacillus polymyxa KF-1: Cloning, Expression and Characterization

Pectate lyase (EC 4.2.2.2) catalyzes the cleavage of α-1,4-glycosidic bonds of pectin polymers, and it has potential uses in the textile industry. In this study, a novel pectate lyase belonging to polysaccharide lyase family 10 was screened from the secreted enzyme extract of Paenibacillus polymyxa KF-1 and identified by liquid chromatography-MS/MS. The gene was cloned from P. polymyxa KF-1 genomic DNA and expressed in Escherichia coli. The recombinant enzyme PpPel10a had a predicted Mr of 45.2 kDa and pI of 9.41. Using polygalacturonic acid (PGA) as substrate, the optimal conditions for PpPel10a reaction were determined to be 50 °C and pH 9.0, respectively. The K_m, v_max and k_cat values of PpPel10a with PGA as substrate were 0.12 g/L, 289 μmol/min/mg, and 202.3 s⁻¹, respectively. Recombinant PpPel10a degraded citrus pectin, producing unsaturated mono- and oligogalacturonic acids. PpPel10a reduced the viscosity of PGA, and weight loss of ramie (Boehmeria nivea) fibers was observed after treatment with the enzyme alone (22.5%) or the enzyme in combination with alkali (26.3%). This enzyme has potential for use in plant fiber processing.

The purification and characterization of a novel alkali-stable pectate lyase produced by Bacillus subtilis PB1

Pectinase is an important kind of enzyme with many industrial applications, among which pectinases produced by bacteria were scarce compared with fungal sources. In this study, a novel bacterium which produced extracellular pectinase was firstly isolated from flue-cured tobacco leaves and identified as Bacillus subtilis PB1 according to its 16S rRNA gene. The pectinolytic enzyme was purified by ammonium sulfate precipitation, ion-exchange and gel filtration chromatography, after which molecular weight was determined as 43.1 ± 0.5 kDa by SDS-PAGE. Peptide mass fingerprinting of the pectinase by MALDI-TOF MS showed that the purified enzyme shared homology with pectate lyase and was designated as BsPel-PB1. The optimal temperature for BsPel-PB1 was 50 °C. The optimal pH was pH 9.5 for BsPel-PB1 while it had a broad pH stability from 5 to 11. The values of K m and V max were 0.312 mg/mL and 1248 U/mL, respectively. Accordingly, the BsPel-PB1 was a novel alkaline pectate lyase which could find potential application as a commercial candidate in the pectinolytic related industries.

A novel strategy for protein production using non-classical secretion pathway in Bacillus subtilis

BACKGROUND

The Gram-positive bacterium Bacillus subtilis has been widely used as a cell factory for the production of proteins due to its generally regarded as safe (GRAS) nature and secretion capability. Of the known secretory pathways in B. subtilis, the majority of proteins are exported from the cytoplasm by Sec pathway, Tat pathway and ABC transporters, etc. However, the production of heterologous proteins by B. subtilis is unfortunately not that straight forward because of the bottlenecks in classical secretion pathways. The aim of this work is to explore a new method for protein production based on non-classical secretion pathway.

RESULTS

One D-psicose 3-epimerase (RDPE) which converts D-fructose into D-psicose from Ruminococcus sp. 5_1_39BFAA was successfully and substantially secreted into the extracellular milieu without the direction of signal peptide. Subsequently, we demonstrated that RDPE contained no native signal peptide, and the secretion of RDPE was not dependent on Sec or Tat pathway or due to cell lysis, which indicated that RDPE is a non-classically secreted protein. Then, we attempted to evaluate the possibility of using RDPE as a signal to export eighteen reporter proteins into the culture medium. Five of eleven homologous proteins, two of five heterologous proteins from other bacterium and two heterologous proteins of eukaryotic source were successfully secreted into the extracellular milieu at different secretion levels when they were fused to RDPE mediated by a flexible 21-bp linker to keep a distance between two single proteins. Furthermore, the secretion rates of two fusion proteins (RDPE-DnaK and RDPE-RFP) reached more than 50 %. In addition, most of the fusion proteins retained enzyme or biological activity of their corresponding target proteins, and all of the fusions still had the activity of RDPE.

CONCLUSIONS

We found and identified a heterologous non-classically secreted protein RDPE, and showed that RDPE could direct proteins of various types into the culture medium, and thus non-classical protein secretion pathway can be used as a novel secretion pathway for recombinant proteins. This novel strategy for recombinant protein production is helpful to make B. subtilis as a more ideal cell factory for protein production.

Cloning, expression and characterization of a pectate lyase from Paenibacillus sp. 0602 in recombinant Escherichia coli

BACKGROUND

Biotechnological applications of microbial pectate lyases (Pels) in plant fiber processing are considered as environmentally friendly. As such, they become promising substitutes for conventional chemical degumming process. Since applications of Pels in various fields are widening, it is necessary to explore new pectolytic microorganisms and enzymes for efficient and effective usage. Here, we describe the cloning, expression, characterization and application of the recombinant Pel protein from a pectolytic bacterium of the genus Paenibacillus in Escherichia coli.

RESULTS

A Pel gene (pelN) was cloned using degenerate PCR and inverse PCR from the chromosomal DNA of Paenibacillus sp. 0602. The open reading frame of pelN encodes a 30 amino acid signal peptide and a 445 amino acid mature protein belonging to the polysaccharide lyase family 1. The maximum Pel activity produced by E. coli in shake flasks reached 2,467.4 U mL⁻¹, and the purified recombinant enzyme exhibits a specific activity of 2,060 U mg⁻¹ on polygalacturonic acid (PGA). The maximum activity was observed in a buffer with 5 mM Ca²⁺ at pH 9.8 and 65°C. PelN displays a half-life of around 9 h and 42 h at 50°C and 45°C, respectively. The biochemical treatment achieved the maximal reduction of percentage weight (30.5%) of the ramie bast fiber.

CONCLUSIONS

This work represents the first study that describes the extracellular expression of a Pel gene from Paenibacillus species in E. coli. The high yield of the extracellular overexpression, relevant thermostability and efficient degumming using combined treatments indicate its strong potential for large-scale industrial production.