Structure-Based Design of Acetolactate Synthase From Bacillus licheniformis Improved Protein Stability Under Acidic Conditions

Improvement of the fibrinolytic activity, acid resistance and thermostability of nattokinase by surface charge engineering

Nattokinase is a promising thrombolytic drug due to its powerful fibrinolytic effect and few side effects. However, the low fibrinolytic activity and stability of nattokinase have limited its industrial production and oral application. In this study, the basic and neutral amino acid residues on the surface of recombinant nattokinase AprY from Bacillus mojavensis LY-06 (rAprY) were mutated to acidic amino acid residues by surface charge engineering strategy, and two variants K12D and N109D with 92.6 % and 8.4 % increased fibrinolytic activity were obtained. The R45E variant with enhanced acid stability and thermostability was also screened, its acid stability at pH 4 and t1/2 at 55 °C were 3.7-fold and 1.8-fold higher than that of wild type rAprY, respectively. Bioinformatics analysis showed that the increased activities of K12D and N109D variants were related to the increased flexibility of the region around their active centers. The increased rigidity of 97-103 amino acid residues around the active center of R45E may be the reason for its enhanced stability and reduced catalytic activity. The multipoint mutation K12D-N109D (M2)'s catalytic activity did not increase cumulatively, but its pH stability did. The nattokinase variants generated in this study have potential for industrial production and application.

Overall analyses of the reactions catalyzed by acetohydroxyacid synthase/acetolactate synthase using a precolumn derivatization-HPLC method

A precolumn derivatization-HPLC method using 2,4-dinitrophenylhydrazine and 4-nitro-o-phenylenediamine as respective labeling reagents for comprehensive analyses of the reactions catalyzed by acetohydroxyacid synthase (AHAS)/acetolactate synthase (ALS) is developed and evaluated in this research. Comparison with the classic Bauerle' UV assay which can analyze the enzymes only through measurement of acetoin production, the HPLC method shows advantages because it can analyze the enzymes not only via determination of consumption of the substrate pyruvate, but also via measurement of formation of the products including acetoin, 2,3-butanedione, and acetaldehyde in the enzymatic reactions. Thus the results deduced from the HPLC method can reflect the trait of each enzyme in a more precise manner. As far as we know, this is the first time that the reactions mediated by AHAS/ALS using pyruvate as a single substrate are globally analyzed and the features of the enzymes are properly discussed.

Characterization of a Nattokinase from the Newly Isolated Bile Salt-Resistant Bacillus mojavensis LY-06

Nattokinase is a potential new thrombolytic drug because of its strong thrombolytic effect, high safety, and low cost. However, there is no research reporting on bile salt-tolerant nattokinase-producing probiotics. In this study, the bile salt-tolerant nattokinase-producing strain Bacillus mojavensis LY-06 was isolated from local Xinjiang douchi, and the fermentation yield of nattokinase of 1434.64 U/mL was obtained by both a single factor experiment and an orthogonal experiment. A gene responsible for fibrinolysis (aprY) was cloned from the genome of strain Bacillus mojavensis LY-06, and the soluble expression of this gene in Escherichia coli (rAprY, fused with His-tag at C-terminus) was achieved; molecular docking elucidates the cause of insoluble expression of rAprY. The optimal pH and temperature for the fibrinolysis activity of nattokinase AprY fermented by Bacillus mojavensis LY-06 were determined to be pH 6.0 and 50 °C, respectively. However, the optimal pH of rAprY expressed in Escherichia coli was 8, and its acid stability, thermal stability, and fibrinolytic activity were lower than those of AprY. Bioinformatics analysis found that the His-tag carried at the C-terminus of rAprY could affect its acidic stability by changing the isoelectric point and surface charge of the enzyme; in contrast to AprY, changes in the number of internal hydrogen bonds and the flexibility of the loop region in the structure of rAprY resulted in lower fibrinolytic activity and poorer thermal stability.

Biotechnology, Bioengineering and Applications of Bacillus Nattokinase

Thrombosis has threatened human health in past decades. Bacillus nattokinase is a potential low-cost thrombolytic drug without side-effects and has been introduced into the consumer market as a functional food or dietary supplement. This review firstly summarizes the biodiversity of sources and the fermentation process of nattokinase, and systematically elucidates the structure, catalytic mechanism and enzymatic properties of nattokinase. In view of the problems of low fermentation yield, insufficient activity and stability of nattokinase, this review discusses the heterologous expression of nattokinase in different microbial hosts and summarizes the protein and genetic engineering progress of nattokinase-producing strains. Finally, this review summarizes the clinical applications of nattokinase.

Advances in biological production of acetoin: a comprehensive overview

Acetoin, a high-value-added bio-based platform chemical, is widely used in foods, cosmetics, agriculture, and the chemical industry. It is an important precursor for the synthesis of: 2,3-butanediol, liquid hydrocarbon fuels and heterocyclic compounds. Since the fossil resources are becoming increasingly scarce, biological production of acetoin has received increasing attention as an alternative to chemical synthesis. Although there are excellent reviews on the: application, catabolism and fermentative production of acetoin, little attention has been paid to acetoin production via: electrode-assisted fermentation, whole-cell biocatalysis, and in vitro/cell-free biocatalysis. In this review, acetoin biosynthesis pathways and relevant key enzymes are firstly reviewed. In addition, various strategies for biological acetoin production are summarized including: cell-free biocatalysis, whole-cell biocatalysis, microbial fermentation, and electrode-assisted fermentation. The advantages and disadvantages of the different approaches are discussed and weighed, illustrating the increasing progress toward economical, green and efficient production of acetoin. Additionally, recent advances in acetoin extraction and recovery in downstream processing are also briefly reviewed. Moreover, the current issues and future prospects of diverse strategies for biological acetoin production are discussed, with the hope of realizing the promises of industrial acetoin biomanufacturing in the near future.