Optimization of culturing conditions of recombined Escherichia coli to produce umami octopeptide-containing protein

Modification of a Novel Umami Octapeptide with Trypsin Hydrolysis Sites via Homology Modeling and Molecular Docking

Increasing the copy number of peptides is an effective method to genetically engineer recombinant expression and obtain umami peptides in large quantities. However, the umami taste value of multicopy number umami peptides is lower than the single ones, thus limiting the industrial application of recombinantly expressed umami peptides. With aims to solve this problem, modification of an umami beefy meaty peptide (BMP) with trypsin hydrolysis sites was carried out via homology modeling and molecular docking in this study. A total of 1286 modified peptide sequences were created and molecularly simulated for docking with the homology modeling-constructed umami receptor (T1R1/T1R3), and 837 peptides were found to be better docked than the BMP. Afterward, the MLSEDEGK peptide with the highest docking score was synthesized. And umami taste evaluation results demonstrated that this modified peptide was close to that of monosodium glutamate (MSG) and BMP, as confirmed by electronic tongue and sensory evaluation (umami value: 8.1 ± 0.2 for BMP; 8.2 ± 0.3 for MLSEDEGK peptide). Meanwhile, mock trypsin digestion of eight copies of MLSEDEGK peptide results showed that the introduced digestion sites were effective. Therefore, the novel modified BMP in this study has the potential for large-scale production by genetic engineering.

Production of l-Methionine from 3-Methylthiopropionaldehyde and O-Acetylhomoserine by Catalysis of the Yeast O-Acetylhomoserine Sulfhydrylase

l-Methionine is an essential bioactive amino acid with high commercial value for diverse applications. Sustained attentions have been paid to efficient and economical preparation of l-methionine. In this work, a novel method for l-methionine production was established using O-acetyl-homoserine (OAH) and 3-methylthiopropionaldehyde (MMP) as substrates by catalysis of the yeast OAH sulfhydrylase MET17. The OAH sulfhydrylase gene Met17 was cloned from Saccharomyces cerevisiae S288c and overexpressed in Escherichia coli BL21. A 49 kDa MET17 was detected in the supernatant of the recombinant E. coli strain BL21-Met17 lysate with IPTG induction, which exhibited the biological activity of l-methionine biosynthesis from OAH and MMP. The recombinant MET17 was then purified from E. coli BL21-Met17 and used for in vitro biosynthesis of l-methionine. The maximal conversion rate (86%) of OAH to l-methionine catalyzed by purified MET17 was achieved by optimization of the molar ratio of OAH to MMP. The method proposed in this study provides a possible novel route for the industrial production of l-methionine.

Characterization of umami compounds in bone meal hydrolysate

The objective of this research was to identify and characterize the chemical compounds that exhibited monosodium glutamate (MSG)-like taste in the hydrolyzed bone meal produced by using flavourzyme. The free amino acids and peptides in the bone meal hydrolysate were analyzed. The results showed that the glutamic acid and the aspartic acid in the bone meal increased by 13.1 times and 14.2 times, respectively, after the flavourzyme hydrolysis. The peptides' isolation identified six MSG-like peptides in the hydrolysate, including APGPVGPAG, DAINWPTPGEIAH, FLGDEETVR, GVDEATIIEILTK, PAGPVGPVG, and VAPEEHPTL, which should contribute to the taste. The human sensory evaluation results indicated that the six peptides showed MSG-like taste, and the electronic tongue analysis indicated that the six peptides showed sourness, saltiness, bitterness, and astringency. The findings of this study demonstrated that the MSG-like taste of the bone meal hydrolysate should be attributed to the generation of MSG-like amino acids and peptides from the flavourzyme hydrolysis. PRACTICAL APPLICATION: The manuscript describes the umami compounds in the bone meal hydrolysate. The findings from this study should further confirm the feasibility of using bone meal to prepare meat-flavor essence and provide a better understanding of preparing bio-source flavoring peptides, which is very important to the artificial meat development and gene breeding.

Optimization of medium composition to increase the expression of recombinant human interferon-β using the Plackett-Burman and central composite design in E. coli SE1

Recombinant human interferon-β (rhIFN-β) is therapeutically important and new commercially viable approaches are needed for its increased production. In this study, a codon-optimized gene encoding for rhIFN-β_(C17S) protein was designed and expressed in E. coli SE1. As a first step of medium optimization, growth of E. coli as a function of different media components was studied. Subsequently, to optimize the media composition, a response surface methodology (RSM) was used. Our results show that optimized medium (15.0 g/L tryptone, 12.3 g/L meat extract, 1.0 g/L MgSO₄ and 0.5 g/L thiamine along with minimal medium) obtained in this study provide better growth of recombinant cells and the expression level of recombinant protein was ~ 1.7-fold more than Luria-Bertani medium. The optimized medium may be utilized for the large-scale production of rhIFN-β.

Identification of novel umami peptides from myosin via homology modeling and molecular docking

The structure of the umami receptor T1R1/T1R3 was constructed using homology modeling and molecular dynamics, and the interactions between peptides and this umami receptor were studied by molecular docking. The umami intensity of the peptides was also investigated by using an electronic tongue. The results showed that 99.3% of the amino acid residues in the homologous model of the T1R1/T1R3 heterodimer were within the allowable range, which is greater than the threshold requirement of 90% of the residues in the high-quality model structure. Five novel peptides (DK, EEK, EDQK, SEGGR, and QDSIGS) were selected and synthesized. The umami intensity of these five peptides was stronger than that of monosodium glutamate. The docking results revealed that the interactions between peptides and the major amino acids residues Arg151, Asp147, and Gln52 of T1R1 play critical roles in the production of umami taste.

Enhancement of extracellular bispecific anti-MUC1 nanobody expression in E. coli BL21 (DE3) by optimization of temperature and carbon sources through an autoinduction condition

Escherichia coli is one of the most suitable hosts for production of antibodies and antibody fragments. Antibody fragment secretion to the culture medium improves product purity in cell culture and diminishes downstream costs. In this study, E. coli strain BL21 (DE3) harboring gene encoding bispecific anti-MUC1 nanobody was selected, and the autoinduction methodology for expression of bispecific anti-MUC1 nanobody was investigated. Due to the replacement of IPTG by lactose as inducer, less impurity and toxicity in the final product were observed. To increase both intracellular and extracellular nanobody production, initially, the experiments were performed for the key factors including temperature and duration of protein expression. The highest amount of nanobody was produced after 21 h at 33°C. The effect of different carbon sources, glycerol, glucose, lactose, and glycine as a medium additive at optimum temperature and time were also assessed by using response surface methodology. The optimized concentrations of carbon sources were obtained as 0.75% (w/v), 0.03% (w/v), 0.1% (w/v), and 0.75% (w/v) for glycerol, glucose, lactose, and glycine, respectively. Finally, the production of nanobody in 2 L fermenter under the optimized autoinduction conditions was evaluated. The results show that the total titer of 87.66 µg/mL anti-MUC1 nanobody, which is approximately seven times more than the total titer of nanobody produced in LB culture medium, is 12.23 µg/L .

Production of Methionol from 3-Methylthiopropionaldehyde by Catalysis of the Yeast Alcohol Dehydrogenase Adh4p

Methionol is a sulfur-containing aroma compound that contributes to the flavors of fermented foods. In this work, a novel method for methionol production was established using 3-methylthiopropionaldehyde (MMP) and alcohol dehydrogenase (ADH). First, expression of seven ADH genes was analyzed in yeast fermentation added with MMP. Only ADH4 displayed an evident increased expression in response to MMP. ADH4 was then overexpressed in Saccharomyces cerevisiae S288c and Escherichia coli BL21. The recombinant yeast strain S4 produced more methionol than control strain in MMP fermentation. Furthermore, 0.55 g/L 42 kDa Adh4p was prepared from E. coli by induced expression and purification. A fed-batch catalysis system was finally established to produce methionol from MMP by Adh4p. In 10 h of continuous catalysis, the conversion rate of MMP remained 80-95%, and a final yield of 0.2 g/L methionol was achieved. This work proposed a novel method for methionol production by enzymatic catalysis with a potential application prospect in industry.

An auto-inducible expression and high cell density fermentation of Beefy Meaty Peptide with Bacillus subtilis

Currently, some cases about the expression of flavor peptides with microorganisms were reported owing to the obvious advantages of biological expression over traditional methods. However, beefy meaty peptide (BMP), the focus of umami peptides, has neither been concerned in its safe expression nor its overproduction in fermenter. In this study, multi-copy BMP (8BMP) was successfully auto-inducibly expressed and efficiently produced in Bacillus subtilis 168. First, 8BMP was successfully auto-inducibly expressed with srfA promoter in B. subtilis 168. Further, the efficient production of 8BMP was researched in a 5-L fermenter: the fermentation optimized by Pontryagin's maximum principle obtained the highest 8BMP yield (3.16 g/L), which was 1.2 times and 1.8 times than that of two-stage feeding cultivation (2.67 g/L) and constant-rate feeding cultivation (1.75 g/L), respectively. Overall, the auto-inducible expression of 8BMP in B. subtilis and fermentation with Pontryagin's maximum principle are conductive for overproduction of BMP and other peptides.

Novel Method for l-Methionine Production Catalyzed by the Aminotransferase ARO8 from Saccharomyces cerevisiae

The aminotransferase ARO8 was proved to play an efficient role in conversion of l-methionine into methionol via the Ehrlich pathway in Saccharomyces cerevisiae in our previous work. In this work, the reversible transamination activity of ARO8 for conversion of α-keto-γ-(methylthio) butyric acid (KMBA) into l-methionine was confirmed in vitro. ARO8 was cloned from S. cerevisiae S288c and overexpressed in Escherichia coli BL21. A 2-fold higher aminotransferase activity was detected in the recombinant strain ARO8-BL21, and ARO8 was detected in the supernatant of ARO8-BL21 lysate with IPTG induction by SDS-PAGE analysis. The recombinant ARO8 was then purified and used for transforming KMBA into l-methionine. An approximately 100% conversion rate of KMBA into l-methionine was achieved by optimized enzymatic reaction catalyzed by ARO8. This work fulfilled l-methionine biosynthesis catalyzed by the aminotransferase ARO8 using glutamate and KMBA, which provided a novel method for l-methionine production by enzymatic catalysis with the potential application prospect in industry.

The expression and construction of engineering Escherichia coli producing humanized AluY RNAs

BACKGROUND

Exogenous RNAs can specifically up-regulate or down-regulate gene expression after they enter into cells. Alu RNAs are the main constituent of human transcriptome and participate in gene expression regulation. AluY elements belong to a subfamily of Alus and are the youngest Alus. In this paper, we established the technology method of preparing genetically engineered humanized AluY RNAs (AluY RNAs) from Escherichia coli (E. coli) strains. This technology method also can be used to prepare other genetically engineered humanized RNAs that can be used for cytology experiments.

RESULTS

Different copies of human AluY elements were inserted into pET-28α plasmid (pET) to construct pET-AluY plasmids that were transformed into BMBL21-DE3 (DE3) E. coli. Isopropylthio-β-D-galactoside (IPTG) induction inhibited transformed bacterial growth after DE3 E. coli were transformed by pET-AluY × 8 plasmid (8 copies of AluYs were inserted into pET); northern blotting was used to detect the amount of AluY RNAs after 2, 4, 6, 8, 10, 12, 14 and 16 h inducing with IPTG. The results showed that the amount of AluY RNAs was the highest at 4 h; 1, 2, 4, 8 or 14 copies of AluY elements were inserted into the pET to construct pET-AluY plasmids that were transformed into DE3 bacteria, the northern blotting results showed that AluY RNAs production amount increased with the increase of AluY copy number; pET-AluY × 8 DE3 bacteria did not produce AluY RNAs without IPTG induction, AluY RNA production kept similar when inducing by 0.1-0.4 mg/ml IPTG induction, however, AluY RNA production slightly decreased if deviating from the above concentration range; pET-AluY × 8 DE3 bacteria were cultured at 34, 37 or 40 °C and the results showed that AluY RNA production was the highest under 37 °C cultivation; pET-AluY × 8 plasmid was transformed into three kinds of BL21 bacteria, including DE3, BMBL21-DE3-pLysS (pLysS) and Trans BL 21 (TransBL), the results showed that AluY RNA production was the highest when using DE3 bacteria.

CONCLUSIONS

The optimal conditions of producing AluY RNAs were: a kind of host bacteria of DE3, an engineering bacteria concentration of OD₆₀₀ 1.0, an IPTG concentration of 0.2 mg/ml, a culturing temperature of 37 °C and a culturing time of 4 h. Pure AluY RNAs occupied 15.8% of extractive total RNAs and the mean yield of pure AluY RNAs in 100 ml bacteria solution was 0.46 mg.

Preparation of umami octopeptide with recombined Escherichia coli: Feasibility and challenges

The taste of umami peptide H-Lys-Gly-Asp-Glu-Glu-Ser-Leu-Ala-OH (LGAGGSLA) is controversial. One possible reason for this controversy is the use of chemically synthesized LGAGGSLA to confirm its taste. To explore other ways to further confirm the flavor of LGAGGSLA, we developed a new strategy to prepare a bio-source peptide by adopting a gene engineering method to express LGAGGSLA in recombinant Escherichia coli. In our previous work, we structured the LGAGGSLA recombinant expression system and optimized the culturing conditions for preparing a fusion protein. However, the fusion protein was not cleaved by enterokinase to obtain LGAGGSLA. Because the cleavage conditions of commercial enterokinase were not specific and recombinant engineered bacteria had the potential to be used in industrial processes, in this addendum, we calculated the mass and volume yields of key processing steps in the preparation of LGAGGSLA, and established a model of cleavage conditions with the cleavage ratio of LGAGGSLA. When the LGAGGSLA was confirmed to show umami taste, it is considered as a new umami or umami enhancer. The gene information of LGAGGSLA should have a great potential in the development of new flavor product and food product containing high umami flavor.