Enhancing extracellular production of lipoxygenase in Escherichia coli by signal peptides and autolysis system

High-Level Extracellular Production of a Trisaccharide-Producing Alginate Lyase AlyC7 in Escherichia coli and Its Agricultural Application

Alginate oligosaccharides (AOS), products of alginate degradation by endotype alginate lyases, possess favorable biological activities and have broad applications. Although many have been reported, alginate lyases with homogeneous AOS products and secretory production by an engineered host are scarce. Herein, the alginate lyase AlyC7 from Vibrio sp. C42 was characterized as a trisaccharide-producing lyase exhibiting high activity and broad substrate specificity. With PelB as the signal peptide and 500 mM glycine as the additive, the extracellular production of AlyC7 in Escherichia coli reached 1122.8 U/mL after 27 h cultivation in Luria-Bertani medium. The yield of trisaccharides from sodium alginate degradation by the produced AlyC7 reached 758.6 mg/g, with a purity of 85.1%. The prepared AOS at 20 μg/mL increased the root length of lettuce, tomato, wheat, and maize by 27.5%, 25.7%, 9.7%, and 11.1%, respectively. This study establishes a robust foundation for the industrial and agricultural applications of AlyC7.

Functional small peptides for enhanced protein delivery, solubility, and secretion in microbial biotechnology

In microbial biotechnology, there is a constant demand for functional peptides to give new functionality to engineered proteins to address problems such as direct delivery of functional proteins into bacterial cells, enhanced protein solubility during the expression of recombinant proteins, and efficient protein secretion from bacteria. To tackle these critical issues, we selected three types of functional small peptides: cell-penetrating peptides (CPPs) enable the delivery of diverse cargoes into bacterial cytoplasm for a variety of purposes, protein-solubilizing peptide tags demonstrate remarkable efficiency in solubilizing recombinant proteins without folding interference, and signal peptides play a key role in enabling the secretion of recombinant proteins from bacterial cells. In this review, we introduced these three functional small peptides that offer effective solutions to address emerging problems in microbial biotechnology. Additionally, we summarized various engineering efforts aimed at enhancing the activity and performance of these peptides, thereby providing valuable insights into their potential for further applications.

Extracellular Expression of Feruloyl Esterase and Xylanase in Escherichia coli for Ferulic Acid Production from Agricultural Residues

There is still a large amount of ferulic acid (FA), an outstanding antioxidant, present in agricultural residues. Enzymatic hydrolysis has been regarded as the most effective way to release FA. This present study therefore selected feruloyl esterase (FAE) and xylanase (XYN) from the metagenomes of a cow rumen and a camel rumen, respectively, for their recombinant expression in Escherichia coli BL21 and further application in releasing FA. After screening the candidate signal peptides, the optimal one for each enzyme, which were selected as SP1 and SP4, respectively, was integrated into the vectors pET22b(+) and pETDuet-1. Among the generated E. coli strains SP1-F, SP4-X, and SP1-F-SP4-X that could express extracellular enzymes either separately or simultaneously, the latter one performed the best in relation to degrading the biomass and releasing FA. Under the optimized culture and induction conditions, the strain SP1-F-SP4-X released 90% of FA from 10% of de-starched wheat bran and produced 314.1 mg/L FA, which was deemed to be the highest obtained value to the best of our knowledge. This result could pave a way for the re-utilization of agricultural residues and enhancing their add-value.

Development of a Bacterial FhuD-Lysozyme-SsrA Mediated Autolytic (FLSA) System for Effective Release of Intracellular Products

Developing effective bacterial autolytic systems for fast release of intracellular bioproducts could simplify purification procedures and help with the high throughput screening of mutant libraries in protein engineering. Here, we developed a fast and tightly regulated E. coli autolytic system, named the FhuD-lysozyme-SsrA mediated autolytic (FLSA) system, by integrating the secretion signal peptide, T7 lysozyme, and E. coli ClpX/P-SsrA protein degradation machinery. To decrease the cytotoxicity of leaky T7 lysozymes, the SsrA tag was fused to the C-terminus of T7 lysozyme to confer a tight regulation of its production. Using sfGFP as a reporter, we demonstrated that anchoring the Sec-Tat dual pathway signal peptide FhuD to the N-terminus of T7 lysozyme-SsrA could give the highest cell lysing efficiency. The optimization of the FLSA system indicated that weak alkaline conditions (pH 8.0) and 0.5% Triton X-100 could further increase the lysing efficiency by about 24%. The FLSA system was validated by efficient production of sfGFP and human growth hormone 1 (hGH1) in a shake flask, with a cell lytic efficiency of approximately 82% and 80%, respectively. Besides, the FLSA system was applied for large-scale fermentation, in which approximately 90% sGFP was released with a cell density OD₆₀₀ of 110. Moreover, the FLSA system was also tested for α-amylase mutant library screening in microplates, and the results showed that intracellular α-amylase can be efficiently released out of cells for activity quantitation. In all, the FLSA system can facilitate the release of intracellular recombinant proteins into the cell culture medium, which has the potential to serve as an integrated system for large-scale production of recombinant targets and high throughput enzyme engineering in synthetic biology.

Efficient extracellular production of recombinant proteins in E. coli via enhancing expression of dacA on the genome

D, D-carboxypeptidase DacA plays an important role in the synthesis and stabilization of Escherichia coli cell wall peptidoglycan. The production level of extracellular recombinant proteins in E. coli can be enhanced by high D, D-carboxypeptidase activity. Construction of expression systems under optimal promoters is one of the main strategies to realize high protein production in E. coli. In this study, the promoter P_dacA-3 from DacA on the genome of E. coli BL21 (DE3) was verified to be efficient for recombinant green fluorescent protein using the plasmid mutant pET28a-P_dacA with P_dacA-3. Meanwhile, the promoter P_dacA-3 was engineered to increase the production level of proteins via inserting one or two Shine–Dalgarno (SD) sequences between the promoter P_dacA-3 and the target genes. The expression level of dacA on the genome was increased by the improved transcription of the engineered promoters (especially after inserting one additional SD sequence). The engineered promoters increased cell membrane permeabilities to significantly enhance the secretion production of extracellular recombinant proteins in E. coli. Among them, the extracellular recombinant amylase activities in E. coli BL21::1SD-pET28a-amyK and E. coli BL21::2SD-pET28a-amyK were increased by 2.0- and 1.6-fold that of the control (E. coli BL21-pET28a-amyK), respectively. Promoter engineering also affected the morphology and growth of the E. coli mutants. It was indicated that the engineered promoters enhanced the expression of dacA on the genome to disturb the synthesis and structural stability of cell wall peptidoglycans.