Extracellular production of active-form Streptomyces mobaraensis transglutaminase in Bacillus subtilis

Efficient Production of a Thermostable Mutant of Transglutaminase by Streptomyces mobaraensis

The transglutaminase (TGase) from Streptomyces mobaraensis is widely used to improve the texture of protein-based foods. However, wild-type TGase is not heat-resistant, which is unfavorable for its application. In this study, we successfully constructed a S. mobaraensis strain that can efficiently produce TGm2, a thermostable mutant of S. mobaraensis TGase. First, S. mobaraensis DSM40587 was subjected to atmospheric room temperature plasma mutagenesis, generating mutant smY2022 with a 12.2-fold increase in TGase activity. Then, based on the double-crossover recombination, we replaced the coding sequence of the TGase with that of TGm2 in smY2022, obtaining the strain smY2022-TGm2. The extracellular TGase activity of smY2022-TGm2 reached 61.7 U/mL, 147% higher than that of smY2022. Finally, the catalytic properties of TGm2 were characterized. The half-life time at 60 °C and specific activity of TGm2 reached 64 min and 71.15 U/mg, 35.6- and 2.9-fold higher than those of the wild-type TGase, respectively. As indicated by SDS-PAGE analysis, TGm2 exhibited demonstrably better protein cross-linking ability than the wild-type TGase at 70 °C, although both enzymes shared a similar ability at 40 °C. With improved enzyme production and thermal stability, smY2022-TGm2 could be a competitive strain for the industrial production of transglutaminase.

Chaperonin co-expression and chemical modification enables production of active microbial transglutaminase from E. coli cytoplasm

Microbial transglutaminase (MTG) is a usable enzyme for biomacromolecule modification. In the present study, a "molecular chaperonin" strategy was developed to produce MTG in E. coli cytoplasm with high expression level and a "small molecule-mediated chemical modification" strategy was adopted to strip propeptide chaperonin efficiently during purification. Propeptide (Pro) was expressed separately as a chaperonin to facilitate MTG expression in E. coli cytoplasm with a yield up to 300 mg or about 9 kU from 1 L fed-batch culture. Furthermore, small molecular chemicals were applied to interfere the interaction between MTG and Pro. Chemical acetylation was identified as a suitable method to strip Pro resulting in pure MTG with high specific activity up to 49.6 U/mg. The purified acetylated MTG was characterized by MS analysis. The deconvoluted mass and Peptide Sequence Tags analysis confirmed acetylation on amino groups of MTG protein. Finally, the applications of obtained MTG were demonstrated via protein polymerization of bovine serum albumin and PEGylation of human interferon-α2b. Our method provides MTG with high purity and specific activity as well as unique merit with masked amino groups thus avoiding self-polymerization and cross-linking between MTG and substrates.

Transglutaminase in Foods and Biotechnology

Stabilization and reusability of enzyme transglutaminase (TGM) are important goals for the enzymatic process since immobilizing TGM plays an important role in different technologies and industries. TGM can be used in many applications. In the food industry, it plays a role as a protein-modifying enzyme, while, in biotechnology and pharmaceutical applications, it is used in mediated bioconjugation due to its extraordinary crosslinking ability. TGMs (EC 2.3.2.13) are enzymes that catalyze the formation of a covalent bond between a free amino group of protein-bound or peptide-bound lysine, which acts as an acyl acceptor, and the γ-carboxamide group of protein-bound or peptide-bound glutamine, which acts as an acyl donor. This results in the modification of proteins through either intramolecular or intermolecular crosslinking, which improves the use of the respective proteins significantly.

Secretion of Bacillus amyloliquefaciens Transglutaminase from Lactococcus lactis and Its Enhancement of Food Gel Properties

(1) Background: Microbial transglutaminases (MTGase) catalyze protein crosslink. This is useful in the food industry to improve gelation, water holding capacity, and emulsifying capacity during foodstuff manufacturing. The production of MTGase in wild-type strains renders low yield and high costs of downstream purification, limiting its industrial applications. (2) Methods: In this work, MTGase from Bacillus amyloliquefaciens BH072 (BaMTGase) has been heterologously expressed in Lactococcus lactis, using the signal peptide Usp45 to direct the secretion of recombinant BaMTGase out of the cell for easier purification. (3) Results: In these conditions, MTGase was purified with a high yield (48.7 ± 0.2 mg/L) and high enzyme activity (28.6 ± 0.5 U/mg). Next, BaMTGase was tested for industrial applications. Recombinant BaMTGase and commercial MTGase were used for SPI solution crosslinking. BaMTGase formed a harder gel with higher water-holding capacity and a dense and smooth gel microstructure. (4) Conclusions: This work provides an attractive food-grade cell factory for the food industry and offers a suitable chassis for MTGase production.

Biocontrol of Candida albicans by Antagonistic Microorganisms and Bioactive Compounds

Candida albicans is an endogenous opportunistic pathogenic fungus that is harmless when the host system remains stable. However, C. albicans could seriously threaten human life and health when the body’s immune function declines or the normal flora is out of balance. Due to the increasing resistance of candidiasis to existing drugs, it is important to find new strategies to help treat this type of systemic fungal disease. Biological control is considered as a promising strategy which is more friendly and safer. In this review, we compare the bacteriostatic behavior of different antagonistic microorganisms (bacteria and fungi) against C. albicans. In addition, natural products with unique structures have attracted researchers’ attention. Therefore, the bioactive nature products produced by different microorganisms and their possible inhibitory mechanisms are also reviewed. The application of biological control strategies and the discovery of new compounds with antifungal activity will reduce the resistance of C. albicans, thereby promoting the development of novel diverse antifungal drugs.

The multifunctionality of expression systems in Bacillus subtilis: Emerging devices for the production of recombinant proteins

Bacillus subtilis is a successful host for producing recombinant proteins. Its GRAS (generally recognized as safe) status and its remarkable innate ability to absorb and incorporate exogenous DNA into its genome make this organism an ideal platform for the heterologous expression of bioactive substances. The factors that corroborate its value can be attributed to the scientific knowledge obtained from decades of study regarding its biology that has fostered the development of several genetic engineering strategies, such as the use of different plasmids, engineering of constitutive or double promoters, chemical inducers, systems of self-inducing expression with or without a secretion system that uses a signal peptide, and so on. Tools that enrich the technological arsenal of this expression platform improve the efficiency and reduce the costs of production of proteins of biotechnological importance. Therefore, this review aims to highlight the major advances involving recombinant expression systems developed in B. subtilis, thus sustaining the generation of knowledge and its application in future research. It was verified that this bacterium is a model in constant demand and studies of the expression of recombinant proteins on a large scale are increasing in number. As such, it represents a powerful bacterial host for academic research and industrial purposes.

Intein-mediated intracellular production of active microbial transglutaminase in Corynebacterium glutamicum

The microbial transglutaminase (mTGase) from Streptomyces mobaraense is widely used in the food industry. However, recombinant production of mTGase is challenging because the mTGase is synthesized as an inactive zymogen, and needs to be activated by proteolytic processing. In this study, self-cleaving intein Ssp DnaB was applied to activate the mTGase in Corynebacterium glutamicum. Premature cleavage of intein Ssp DnaB also occurred, but instead of suppressing premature cleavage, this phenomenon was used to produce active mTGase in C. glutamicum. Both SDS-PAGE analysis and mTGase activity assays indicated that the premature cleavage of intein Ssp DnaB activated the mTGase intracellularly in C. glutamicum. The subsequent N-terminal amino acid sequencing and site-directed mutagenesis studies further showed that the premature cleavage activated the mTGase intracellularly, in a highly specific manner. Moreover, the growth performance of C. glutamicum was not noticeably affected by the intracellular expression of active mTGase. Finally, the mTGase was produced in a 2 L bioreactor, with activity up to 49 U/mL, the highest intracellular mTGase activity ever reported. Using premature cleavage of intein Ssp DnaB to activate mTGase in C. glutamicum, we produced high levels of intracellular active mTGase. Moreover, this approach did not require any further processing steps, such as protease treatment or lengthy incubation, greatly simplifying the production of active mTGase. This efficient and simple approach has great potential for the large-scale industrial production of active mTGase.

Maltose Induced Expression of Cecropin AD by SUMO Technology in Bacillus subtilis WB800N

Cecropin AD (CAD) is a hybrid peptide composed of 37 amino acids with the characters of strong antibacterial, antitumor properties and no hemolytic activity, which was regarded as a promising antibiotic candidate. Thus, a safe method to produce Cecropin AD is necessary to be found. In the study, Bacillus subtilis WB800N was employed as host strain. The CAD coding sequence fused with the signal peptide of SP_sacB, the 6 × His gene and the gene of small ubiquitin-like modifier were cloned into the maltose-inducible vector pGJ148. Under the induction by 6% maltose, the recombinant fusion protein was successfully expressed and detected in culture substrate. An optimized amount (26.4 mg/L) of the recombinant CAD was purified of culture supernatant. After purification and digestion, the recombinant CAD was harvested about 4.5 mg/L with a purity of 93%. Recombinant CAD exhibited similar antimicrobial activity with synthetic CAD. This shows that the production of CAD in maltose-induced Bacillus subtilis expression system is a relatively safe method, which is vital for the application of CAD in animal husbandry production.