Patent Application
20190376100
The present disclosure relates to an engineering strain and application thereof in production of Danshensu, and belongs to the technical field of bioengineering.
Danshensu extracted from Salvia miltiorrhiza, has scientific names of R-(+)-3-(3,4-dihydroxyphenyl)-2-hydroxypropanoic acid and D-(+)-6-(3,4-dihydroxyphenyl) lactic acid, has English names of danshensu, D-DSS, R-DSS, (R)-(+)-3-(3,4-dihydroxyphenyl)-lactic acid, and (R)-(+)-3-(3,4-dihydroxyphenyl)-2-hydroxypropanoic acid, and is a dextrophenolic acid compound. Currently, there is no natural L-danshensu.
Danshensu is an important active ingredient in a water extract ofSalvia miltiorrhiza, and the structure in the water extract of Salvia miltiorrhiza was obtained and identified in China in 1980 (Study on Water-soluble Active Ingredients of Salvia miltiorrhiza, Structure of II.D(+)6(3,4-Dihydroxyphenyl)Lactic Acid, Shanghai First Medical College Journal, 1980, 05(7), 384-385). Various studies have shown that Danshensu has important pharmacological effects and has unique effects in treatment of cardiovascular and cerebrovascular diseases.
At present, Danshensu is mainly extracted from Salvia miltiorrhiza (patent CN200810038853.9). The content of Danshensu in Salvia miltiorrhiza is low, the cost for planting Salvia miltiorrhiza is high, and the yield is limited. Therefore, Danshensu is not only expensive but also far from meeting the market demand. Patent CN201310559498.0 proposes a method for constructing Escherichia coli genetically engineered strain to produce Danshensu by glucose fermentation. Since the anabolic pathway involves the use of a hydroxylase, the enzyme is likely to oxidize a metabolic process product and affect the yield of Danshensu. At the same time, because E. coli fermentation is a high oxygen consumption process, it also oxidizes Danshensu. Therefore, the current method has lower yield, and the cost will be higher than that of a plant extraction process. Patent CN201210190171.6 proposes a method for producing Danshensu by hydrolyzing salvianolic acid B. Salvianolic acid B needs to be extracted from Salvia miltiorrhiza, and the chemical hydrolysis process has a large number of side reactions, which is also not suitable for large-scale production. A catalyst for chiral synthesis of Danshensu (patent CN201210420488.4) is extremely expensive and currently only stays at the laboratory level.
As early as 1988, Roth et al. proposed a method for treating levodopa by a chemical method to obtain the corresponding 3,4-dihydroxyphenylpyruvic acid, and then synthesizing S-(+)-3-(3,4-dihydroxyphenyl)-2-hydroxypropanoic acid (S-DSS, L-DSS) by an enzymic method (Enzymatic Synthesis of (S)-(−)-3-(3, 4-Dihydroxyphenyl)lactic Acid, Arch. Pharm. (Weinheim) 321, 179-180 (1988)). Z. Findrik, et al. used snake venom amino acid oxidase to convert levodopa into 3,4-dihydroxyphenylpyruvic acid, then used D-lactate dehydrogenase for reduction to produce D-(3,4-dihydroxyphenyl)lactic acid (Modelling and Optimization of the (R)-(+)-3,4-dihydroxyphenyllactic Acid Production Catalyzed with D-lactate dehydrogenase from Lactobacillus leishmannii Using Genetic Algorithm, Chem. Biochem. Eng. Q. 19 (4) 351-358 (2005)). Preparation of the 3,4-dihydroxyphenylpyruvic acid intermediate by the two methods is costly and complicated in operation.
Based on the defects of various current methods, the present disclosure provides an optically pure Danshensu production method based on transaminase, and constructs a multi-enzyme co-expression engineering strain to achieve efficient production of Danshensu. The present disclosure provides a recombinant strain which can produce Danshensu at a low cost. At the same time, the present disclosure also provides the construction and application of the strain.
The present disclosure is firstly directed to a recombinant strain which can produce optically pure Danshensu at a low cost. The recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase and L-α-amino acid transaminase, and any one of the following: glucose dehydrogenase, L-lactate dehydrogenase, and L-glutamate dehydrogenase, and a gene related to decomposition of phenolic compounds is knocked out on the basis of a host E. coli.
In an example, the α-hydroxycarboxylate dehydrogenases are D-α-hydroxycarboxylate dehydrogenase, and are from Lactobacillus plantarum ATCC 14917, Enterococcus faecalis ATCC 35038 or Lactobacillus fermentum ATCC 14931.
In an example, the α-hydroxycarboxylate dehydrogenases are L-α-hydroxycarboxylate dehydrogenase, and are from Bacillus coagulans DSM 1, Weissella confusa strain DSM 20196, or Lactobacillus fermentum ATCC 14931.
In an example, the α-hydroxycarboxylate dehydrogenases are D-α-hydroxycarboxylate dehydrogenase, of which the amino acid sequences have an accession NO of WP_003643296.1, WP_002335374.1, or EEI 122188.1 on NCBI; α-hydroxycarboxylate dehydrogenases are L-α-hydroxycarboxylate dehydrogenase, of which the amino acid sequences have accession NO of WP_013858488.1, WP_003607654.1 or WP_035430779.1 on NCBI.
In an example, the nucleotide sequences of D-α-hydroxycarboxylate dehydrogenase have accession NO. of NZ_GL379761 REGION: COMPLEMENT(533562 . . . 534560), NZ_KB944641 REGION: 161892 . . . 162830, or ACGI01000078 REGION: 20793 . . . 21791 on NCBI; the nucleotide sequences of L-α-hydroxycarboxylate dehydrogenase have accession NO. of NZ_ATUM01000014 REGION: 39316 . . . 40254, NZ_JOAY01000006 REGION: 69708 . . . 70640, or NZ_GG669901 REGION: 45517 . . . 46470 on NCBI.
In an example, the L-α-amino acid transaminases are from E. coli BL21, Lactobacillus plantarum ATCC 14917, or Lactobacillus paracasei ATCC 334.
In an example, the amino acid sequences of L-α-amino acid transaminase have accession NO of WP_000462687.1, WP_000486988.1, WP_003643296.1, or YP_806114.1 on NCBI.
In an example, the nucleotide sequences of L-α-amino acid transaminase have accession NO of NC_012892 REGION: COMPLEMENT (989603 . . . 990793), NC_012892 REGION: 4174517 . . . 4175710, NZ_GL379768 REGION: complement (121900 . . . 123087), or NC_008526 REGION: complement (840419 . . . 841594) on NCBI.
In an example, the glucose dehydrogenase is from Bacillus subtilis ATCC 13952.
In an example, the amino acid sequence of the glucose dehydrogenase has an accession NO of WP_013351020.1 on NCBI.
In an example, the nucleotide sequence of the glucose dehydrogenase has an accession NO of NZ_CP009748 REGION: 386154 . . . 38693 on NCBI.
In an example, the L-lactate dehydrogenase is from Lactococcus lactic ATCC 19257.
In an example, the amino acid sequence of the L-lactate dehydrogenase has an accession NO of WP_003131075.1 on NCBI.
In an example, the nucleotide sequence of the L-lactate dehydrogenase has an accession NO of NZ_JXJZ01000017 REGION: 18532 . . . 19509 on NCBI.
In an example, the L-glutamate dehydrogenases are from E. coli BL21, Rhodobacter sphaeroides ATCC BAA-808, Clostridium symbiosum ATCC 14940, or Bacillus subtilis 168.
In an example, the amino acid sequences of the L-glutamate dehydrogenase have accession NO of WP_000373021.1, WP_011338202.1, WP_003497202.1, or WP__010886557.1 on NCBI.
In an example, the nucleotide sequences of L-glutamate dehydrogenase have accession NO of NC_012892 REGION: 1786741 . . . 1788084, NC_007493 REGION: complement (2129131 . . . 2130558), NZ_KE992901 REGION: complement (17603 . . . 18955), or NC_000964 REGION: complement (2402067 . . . 2403350) on NCBI.
In an example, the recombinant strain is a recombinant engineering strain obtained by ligating genes encoding L-α-amino acid transaminase, α-hydroxycarboxylate dehydrogenase and any one of glucose dehydrogenase, L-lactate dehydrogenase and L-glutamate dehydrogenase to a plasmid to construct a three-gene co-expression recombinant plasmid, and then transforming the recombinant plasmid into a corresponding strain.
In an example, the recombinant strain is constructed by using E. coli BL21 (DE3) as a host.
In an example, the gene related to decomposition of the phenol compounds is any one or a combination of hpaD and mhpB.
In an example, the nucleotide sequences of the phenolic substance decomposing gene have accession NO of NC_012892 REGION: complement (4505585 . . . 4506436) and NC_012892 REGION: 339806 . . . 340750 on NCBI.
In an example, the recombinant strain further enhances expression of one or more of a pyruvic acid transporter gene, an L-lactic acid transporter gene, a glutamic acid transporter gene, an NAD synthesis gene, and a pyridoxal phosphate synthesis gene, where the pyruvic acid transporter genes, the L-lactic acid transporter gene and the glutamic acid transporter gene are not expressed at the same time.
In an example, enhanced expression is to add a constitutive promoter ahead of the gene to be enhanced in expression on an E. coli BL21 (DE3) genome.
In an example, the gene to be enhanced in expression is any one or more of the pyruvic acid transport-related genes, IldP (lactic acid transporter gene), gltS (glutamic acid transporter gene), nadA (NAD synthetic gene) and pdxJ (pyridoxal phosphate synthesis gene), where the pyruvic acid transport-related genes include btsT and ybdD (gene for transporting pyruvic acid into cells).
In an example, the accession NOs of btsT and ybdD on NCBI are: for nadA, NC_012892 REGION: 740487 . . . 741530; for pdxJ, NC_012892 REGION: complement (2567591 . . . 2568322).
In an example, the accession NO of the IldP on NCBI is: NC_012892 REGION: 3646638 . . . 3648293; for nadA, NC_012892 REGION: 740487 . . . 741530; for pdxJ, N_012892 REGION: complement (2567591 . . . 2568322).
In an example, the accession NO of gltS on NCBI is: NC_012892 REGION: complement (3694931 . . . 3696136); for nadA, NC_012892 REGION: 740487 . . . 741530; for pdxJ, NC_012892 REGION: complement (2567591 . . . 2568322).
The present disclosure provides a method for producing Danshensu using the recombinant strain of the present disclosure.
In an example, the production of Danshensu is carried out by whole cell transformation.
In an example, in a whole cell transformation production system, cell wet weight is 1-200 g/L, and levodopa concentration is 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and glucose dehydrogenase, in the whole cell transformation production system, the pyruvic acid concentration is 1-200 g/L, and the glucose concentration is 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-lactate dehydrogenase, the whole cell transformation production system includes the L-lactic acid of 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-glutamate dehydrogenase, the whole cell transformation production system includes L-glutamic acid of 1-200 g/L.
The whole cell transformation production system has a pH of 6.0-9.0, and reacts at 15-40° C. for 1-48 hours.
The present disclosure constructs a novel multi-enzyme co-expression genetic engineering strain, and realizes low-cost production of Danshensu. Further, transport of a substrate is promoted and decomposition of products is reduced by knocking out or enhancing expression of related genes on the E. coli genome. The (D/L)-α-hydroxycarboxylate dehydrogenase selected by the present disclosure has the characteristics of poor substrate specificity and strong optical specificity, and can produce optically pure D-danshensu and L-danshensu. The production process is simple, raw materials are easily available, and a good industrial application prospect is achieved.
The functional core of the engineering strain provided by the present disclosure is that three enzymes, respectively L-α-amino acid transaminase, α-hydroxycarboxylate dehydrogenase, and any one of glucose dehydrogenase, L-lactate dehydrogenase and L-glutamate dehydrogenase, can be simultaneously expressed. The principle is: in the whole cell of the engineering strain, glucose dehydrogenase or L-lactate dehydrogenase or L-glutamate dehydrogenase uses NAD in the cell as a coenzyme to dehydrogenate the corresponding glucose, or L-lactate dehydrogenase or L-glutamate dehydrogenase generates NADH and corresponding gluconic acid or pyruvic acid or α-ketoglutaric acid; levodopa is deaminated by L-α-amino acid transaminase to generate 3,4-dihydroxyphenylpyruvic acid, and pyruvic acid is converted into alanine by ammonia; α-hydroxycarboxylate dehydrogenase uses NADH produced by the dehydrogenation process of glucose to reduce the 3,4-dihydroxyphenylpyruvic acid into Danshensu and simultaneously regenerate the coenzyme NAD. Further, transport of a substrate is promoted and decomposition of products is reduced by knocking out or enhancing expression of related genes on an E. coli genome.
1. Strains and Plasmids of the Present Disclosure
Lactobacillus plantarum ATCC 14917, Enterococcus faecalis ATCC 35038, Lactobacillus fermentum ATCC 14931, Lactobacillus paracasei ATCC 334, Bacillus subtilis ATCC 13952, E. coli BL21 (DE3) and Lactococcus lactic ATCC 19257 purchased from American Type Culture Collection (ATCC). Bacillus coagulans DSM 1 and Weissella confusa strain DSM 20196 purchased from Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ). PETDuet-1, pACYCDue-1, pCOLADuet-1 and pRSFDuet-1 plasmids and E. coli BL21(DE3) purchased from Novagen.
2. Knockout and Constitutive Enhanced Expression of Related Genes in E. coli
(1) Knockout of Genes Related to Decomposition of Phenolic Compounds in E. coli Phenolic Compound
Phenolic substances in the present disclosure are highly susceptible to decomposition by enzymes in E. coli. According to the literature (Biodegradation of Aromatic Compounds by E. coli, Microbiol Mol Biol Rev. 2001, 65(4): 523-569.), related genes are knocked out to avoid decomposition of products and substrates. The selected genes are hpaD and mhpB, of which the accession NOs on NCBI are NC_012892 REGION: complement (4505585 . . . 4506436) and NC_012892 REGION: 339806 . . . 340750.
(2) Constitutive Enhanced Expression of E. coli Pyruvic Acid Transporter Gene
In the process of whole cell transformation, the substrate needs to be transported into the cell to carry out reaction. Enhancing pyruvic acid transport protein is helpful to rapid and long-term maintenance of high concentration of the intracellular substrate, and is favorable for the progress of the reaction. The selected pyruvic acid transport-related genes are btsT and ybdD, of which the accession NOs on NCBI are NC_012892 REGION: complement (4496239 . . . 4498389) and NC_012892 REGION: 592652 . . . 592849. Dopa is similar to aromatic amino acids, and needs to absorb amino acids and the like during cell culture. Therefore, the cells themselves express a large amount of amino acid transport protein, and need not to enhance expression.
(3) Constitutive Enhanced Expression of Important Genes Related to E. coli Coenzyme Synthesis
In the reduction process of α-hydroxycarboxylate dehydrogenase, NADH needs to be used as a coenzyme. Enhanced expression of key enzymes in an E. coli NAD synthesis pathway can increase the level of NAD in the cells, thereby being beneficial to the production of Danshensu. The selected gene is nadA. The accession NO on NCBI is: NC_012892 REGION: 740487 . . . 741530.
Pyridoxal phosphate (amine) is a coenzyme of L-α-amino acid transaminase, and overexpression of the core gene pdxJ in the coenzyme pathway is beneficial to the synthesis of levodopa. The accession NO on NCBI is: NC_012892 REGION: complement (2567591 . . . 2568322).
3. Enzyme Selection
(1) Selection of L-α-Amino Acid Transaminase
L-α-amino acid transaminase is widely present in bacteria, fungi and mammalian cells. Usually a transaminase with α-ketoglutaric acid or oxaloacetic acid as an ammonia receptor is most active. In this process, the α-ketoglutaric acid or oxaloacetic acid is expensive, while the value of the correspondingly produced glutamic acid or aspartic acid is much lower than that of the corresponding precursor. A comprehensive examination of the corresponding α-keto acids of 20 natural L-amino acids reveals that the prices of pyruvic acid and alanine are comparable. Therefore, the present disclosure selects the pyruvic acid as the ammonia receptor to realize joint production of alanine and Danshensu. The L-α-amino acid transaminase genes lot and la are cloned from Lactobacillus plantarum ATCC 14917 and Lactobacillus paracasei ATCC 334 respectively, and the amino acid sequences thereof have accession NOs of WP_003643296.1 and YP _806114.1 on NCBI. Two L-α-amino acid transaminase genes ectl and ect2 are cloned from E. coli BL1 (DE3), and the amino acid sequences thereof have accession NOs of WP_000462687.1 and WP_000486988.1 on NCBI.
(2) Selection of α-Hydroxycarboxylate Dehydrogenase
According to the optimum substrate, α-hydroxycarboxylate dehydrogenase contains lactate dehydrogenase, aα-hydroxy acid isohexanoate dehydrogenase, mandelic acid dehydrogenase, glyoxylate reductase, etc. These enzymes can act extensively on a variety of substrates to generate α-hydroxycarboxylic acids, usually named according to their substrates of optimum function. The present disclosure selects enzymes which are high in optical property and has a strong activity against 3,4-dihydroxyphenylpyruvic acid, to produce D- or L-danshensu. D-α-hydroxycarboxylate dehydrogenase genes Ipldhd, efmdhd and Ifldhd are respectively cloned from Lactobacillus plantarum ATCC 14917, Enterococcus faecalis ATCC 35038 and Lactobacillus fermentum ATCC 14931, and the amino acid sequences thereof have the accession NOs of WP_003643296.1, WP_002335374.1 and EEl22188.1 on NCBI. L-α-hydroxycarboxylate dehydrogenase genes bcldhl, wcldhl and Ifldhl are respectively obtained from Bacillus coagulans DSM 1, Weissella confusa strain DSM 20196 and Lactobacillus fermentum ATCC 14931, and the amino acid sequences thereof have the accession NOs of WP_013858488.1, WP_003607654.1 and WP_035430779.1 on NCBI.
(3) Selection of Glucose Dehydrogenase
In biotransformation reactions, α-hydroxycarboxylate dehydrogenase requires NADH and/or NADPH as coenzyme, usually formate dehydrogenase, glucose dehydrogenase, phosphite dehydrogenase, etc. Glucose dehydrogenase is the most active compared to other enzymes, and thus the present disclosure obtains the glucose dehydrogenase gene bsgdh (of which the amino acid sequence is WP_013351020.1) from Bacillus subtilis ATCC 13952.
(4) Selection of L-Lactate Dehydrogenase
L-lactic acid is the most inexpensive organic acid, and alanine produced by transamination of pyruvic acid after dehydrogenation has a high added value. L-lactate dehydrogenase is widely present in a variety of microorganisms. Using L-lactic acid as a substrate, hydrogen generated on L-lactic acid is transferred to the coenzyme NAD or NADP to produce NADH or NADPH. NADH or NADPH can be used as a hydrogen donor of the aforementioned α-hydroxylcarboxylic acid dehydrogenase. Generally, lactate dehydrogenase with NADH (NADPH) as a coenzyme tends to synthesize lactic acid with pyruvic acid as a substrate. However, when the lactic acid is excessive, and the like, the lactate dehydrogenase will remove the hydrogen of the lactic acid to produce pyruvic acid. The present disclosure obtains the L-lactate dehydrogenase gene Illdh (of which the amino acid sequence is WP_003131075.1) from Lactococcus lactic ATCC 19257.
(5) Selection of L-Glutamate Dehydrogenase
L-glutamic acid is the most inexpensive amino acid, and α-ketoglutaric acid produced after dehydrogenation can be used as an ammonia receptor for levodopa transamination and deamination. L-glutamate dehydrogenase is widely found in almost all organisms. Using L-glutamic acid as a substrate, hydrogen produced on L-glutamic acid is transferred to the coenzyme NAD or NADP to produce NADH or NADPH. NADH or NADPH can be used as a hydrogen donor of the aforementioned hydroxylcarboxylic acid dehydrogenase. The present disclosure obtains L-glutamic acid genes ecgdh (of which the amino acid sequence is WP_000373021.1), rsgdh (of which the amino acid sequence is WP_011338202.1), csgdh (of which the amino acid sequence is WP_003497202.1) and bsgdh (of which the amino acid sequence is WP_010886557.1) from E. coli BL21, Rhodobacter sphaeroides ATCC BAA-808, Clostridium symbiosum ATCC 14940 and Bacillus subtilis 168, respectively.
4. Construction of Three-Enzyme Co-Expression System and Cell Culture
At present, there are many methods for E. coli multi-gene co-expression (E. coli Multi-gene Co-expression Strategy, China Biotechnology, 2012, 32(4): 117-122). The present disclosure adopts a method described by Liu Xianglei (Production of Shikimic Acid and Resveratrol by Transformation of E. coli by Synthetic Biotechnology, 2016, Shanghai Pharmaceutical Industry Research Institute, Ph.D. Thesis). Each gene contains a T7 promoter and an RBS binding site at the front, and each gene has a T7 terminator at the back. Theoretically, because each gene has T7 and RBS at the front, the expression intensity of the gene is less affected by the order. Each plasmid contains three genes (genes corresponding to L-α-amino acid transaminase, (D/L)-α-hydroxycarboxylate dehydrogenase, and glucose dehydrogenase or L-lactate dehydrogenase or L-glutamate dehydrogenase). The constructed plasmid is heat-transferred into E. coli competent cells, and the E. coli competent cells are coated on an antibiotic solid plate. Positive transformants are obtained by screening, that is, recombinant E. coli is obtained. Cells are cultured according to a classical recombinant E. coli culture and induction expression program. Recombinant E. coli is transferred to an LB fermentation medium (containing peptone of 10 g/L, yeast powder of 5 g/L, and NaCl of 10 g/L) at a volume ratio of 2%.
After the cell OD600 reaches 0.6-0.8, IPTG with a final concentration of 0.4 mM is added, and induction expression and culture are carried out at 20° C. for 8 h. After induction expression is completed, the cells are collected by centrifugation at 20° C. and 8000 rpm for 20 minutes.
5. Whole Cell Transformation Production of Pure Danshensu
In a cell transformation production system, cell wet weight is 1-200 g/L, and levodopa concentration is 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and glucose dehydrogenase, in the whole cell transformation production system, the pyruvic acid concentration is 1-200 g/L, and the glucose concentration is 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-lactate dehydrogenase, the whole cell transformation production system further includes L-lactic acid of 1-200 g/L.
When the recombinant strain simultaneously expresses α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-glutamate dehydrogenase, the whole cell transformation production system further includes L-glutamic acid of 1-200g/L.
The whole cell transformation produces system has a pH of 6.0-9.0, and reacts at 15-40° C. for 1-48 hours.
After the end of transformation, the yield and configuration of Danshensu are determined by liquid chromatography. Levodopa has a low solubility and is a suspension containing an insoluble matter at high concentrations.
6. Detection and Analysis of Samples
Quantitative analysis of Danshensu: The transformed broth is detected and analyzed by a PerkinElmer Series 200 high performance liquid chromatograph with a differential refractive index detector. The chromatographic conditions are as follows: the mobile phase is methanol-0.1% formic acid water (40:60), a Hanbon Megres C18 chromatographic column (4.6×250 mm, 5 μm) is used, the flow rate is 1 ml/min, the column temperature is 30° C., and the injection volume is 20 μl.
Chiral analysis: A PerkinElmer Series 200 high performance liquid chromatograph with a UV detector is used for detection and analysis, a Chiralcel OD-H chiral column (4.6×250mm) is used, the mobile phase volume ratio of n-hexane to isopropanol to trifluoroacetic acid is 80:20:0.1, the flow rate is 0.5 mL/min, the column temperature is 25° C., the injection volume is 20 μl, and the detection wavelength is 280 nm.
Danshensu has a relatively low solubility, and if crystallization appears in the transformation process, measurement is carried out after dilution.
The optical purity of Danshensu is evaluated by an enantiomeric excess value (% e.e).
When R-danshen is produced,
the enantiomeric excess value % e.e=[(SR−SS)/(SR+SS)×100%]
When S-danshen is produced,
the enantiomeric excess value % e.e=[(SS−SR)/(SR+SS)×100%]
where SS is the peak area of S-danshensu in the transformed broth, and SR is the liquid chromatography peak area of R-danshen in the transformed broth.
By a method according to the literature Large scale validation of an efficient CRISPR/Cas-based multi gene editing protocol in E. coli. Microbial Cell Factories, 2017, 16(1):68, HpaD and mhpB on E. coli BL21(DE3) are singly or doubly knocked out. The gene knockout plasmids used in the present disclosure are pCasRed and pCRISPR-gDNA (hpaD sgRNA) which are introduced into E. coli BL21(DE3) together with a homologous arm (hpaD donor). Cas9/sgRNA induces double-strand break in the hpaD gene locus of the host, the recombinase Red integrates the hpaD donor onto the hpaD gene to realize knockout of the gene, and the gene is verified by sequencing. hpaD sgRNA, hpaD donor, mhpB sgRNA and mhpB donor respectively as shown in SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11 and SEQ ID NO:12. MhpB is knocked out in the same way.
A solution having a pH of 7 is prepared with the levodopa or D-danshensu of 4 g/L, the amount of wet cells is 200 g/L, and the concentration is measured after the solution is placed at 35° C. for 10 hours. The residual amounts of levodopa and D-danshensu in the reaction system are shown in Table 1.
E. coli BL21 (DE3)
E. coli BL21 (ΔhpaDΔmhpB, DE3)
E. coli BL21 (ΔhpaD, DE3)
E. coli BL21 (ΔmhpB, DE3)
Obviously, E. coli BL21 (AhpaDAmhpB, DE3) has the best effect and is named E. coli HM.
During screening of L-α-amino acid transaminase, a variety of L-α-amino acid transaminase genes are cloned from E. coli and lactobacilli respectively and expressed in E. coli BL21(DE3). The crude enzyme activity is determined by cell disruption, and the activities of various enzymes are compared with pyruvic acid as a receptor. The activity of L-α-amino acid transaminase is determined according to the literature (Transaminase-catalyzed asymmetric synthesis of aromatic L-amino acids. Chinese Journal of Biotechnology, 2012, 28(11): 1346-1358.). The results are shown in Table 2. Therefore, it is preferred to select L-α-amino acid transaminase ectl derived from E. coli for transamination and deamination of levodopa.
The activities of various enzymes with α-ketoglutaric acid as a receptor are compared. The activity of L-α-amino acid transaminase is determined according to the method described in the literature (Transaminase-catalyzed asymmetric synthesis of aromatic L-amino acids. Chinese Journal of Biotechnology, 2012, 28(11): 1346-1358.). The results are shown in Table 3. Therefore, it is preferred to select L-α-amino acid transaminase lct derived from Lactobacillus paracasei ATCC 334 for transamination and deamination of levodopa.
The induction expression method is: recombinant E. coli is transferred to an LB fermentation medium (containing peptone of 10 g/L, yeast powder of 5 g/L and NaCl of 10 g/L) at a volume ratio of 2%. After the cell OD600 reaches 0.6-0.8, IPTG with a final concentration of 0.4 mM is added, and induction expression and culture are carried out at 20° C. for 8 h. After induction expression is completed, the cells are collected by centrifugation at 20° C. and 8000 rpm for 20 minutes.
E. coli BL21 (DE3)/pETDuet-1-ect1
E. coli BL21 (DE3)/pETDuet-1-ect2
E. coli BL21 (DE3)/pETDuet-1-lpt
E. coli BL21 (DE3)/pETDuet-1-lct
E. coli BL21/pETDuet-1-ect1
E. coli BL21/pETDuet-1-ect2
E. coli BL21/pETDuet-1-lpt
E. coli BL21/pETDuet-1-lct
The enzymatic properties of α-hydroxycarboxylate dehydrogenase are compared. Usually, this enzyme may also have the ability to reduce pyruvic acid to produce lactic acid, so that an enzyme that cannot reduce or very weakly reduces pyruvic acid is preferred. Using pyruvic acid as a substrate, the reducing ability of different enzymes is compared. By a method according to the literature (Study on cloning expression, purification and enzymatic property of Serratia marcescens H3010 fermented D-lactate dehydrogenase gene. Industrial Microbiology, 2012, 42(04):30-37.), the activity of NAD as a coenzyme to reduce pyruvic acid is determined, and the experimental results are shown in Table 4.
E.
coli HM/pETDuet-1-lpldhd
E.
coli HM/pETDuet-1-efmdhd
E.
coli HM/pETDuet-1-lfldhd
E.
coli HM/pETDuet-1-bcldhl
E.
coli HM/pETDuet-1-wcldhl
E.
coli HM/pETDuet-1-lfldhl
The recombinant E. coli simultaneously expressing α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and glucose dehydrogenase is constructed: firstly, genes encoding L-α-amino acid transaminase, α-hydroxycarboxylate dehydrogenase and glucose dehydrogenase are ligated to a plasmid to obtain a three-gene co-expression recombinant plasmid. The plasmid is transformed into E. coli HM, and positive transformants are obtained by screening with an antibiotic plate to obtain recombinant E. coli.
After induction expression of the recombinant E. coli is completed, cells are collected, and in a reaction volume of 100 ml with cell wet weight of 40 g/L, levodopa of 40 g/L, pyruvic acid of 30 g/L, glucose of 30 g/L and pH of 8.0, reaction is carried out at 35° C. for 12 hours. After the end of transformation, the yield and configuration of Danshensu are determined by liquid chromatography, and the results are shown in Table 5.
E.
coli HM/pETDuet-1-wcldhl-ect1-bsgdh
E.
coli HM/pETDuet-1-bcldhl-ect1-bsgdh
E.
coli HM/pETDuet-1-lfldhl-ect1-bsgdh
E.
coli HM/pETDuet-1-efmdhd-ect1-bsgdh
E.
coli HM/pETDuet-1-lpldhd-ect1-1-bsgdh
E.
coli HM/pETDuet-1-lfldhd-ect1-bsgdh
The recombinant E. coli simultaneously expressing α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-lactate dehydrogenase is constructed: firstly, genes encoding the L-lactate dehydrogenase, L-α-amino acid transaminase and α-hydroxycarboxylate dehydrogenase are ligated to a plasmid to obtain a three-gene co-expression recombinant plasmid. The plasmid is transformed into E. coli HM, and positive transformants are obtained by screening with an antibiotic plate to obtain recombinant E. coli.
After induction expression of the recombinant E. coli is completed, cells are collected, and in a reaction volume of 100 ml with cell wet weight of 40 g/L, levodopa concentration of 40 g/L, pyruvic acid concentration of 30 g/L, and pH of 8.0, reaction is carried out at 35° C. for 12 hours. After the end of transformation, the yield and configuration of Danshensu are determined by liquid chromatography, and the results are shown in Table 6.
E.
coli HM/pETDuet-1-wcldhl-ect1-llldh
E.
coli HM/pETDuet-1-bcldhl-ect1-llldh
E.
coli HM/pETDuet-1-lfldhl-ect1-llldh
E.
coli HM/pETDuet-1-efmdhd-ect1-llldh
E.
coli HM/pETDuet-1-lpldhd-ect1-1-llldh
E.
coli HM/pETDuet-1-lfldhd-ect1-llldh
The recombinant E. coli simultaneously expressing α-hydroxycarboxylate dehydrogenase, L-α-amino acid transaminase and L-glutamate dehydrogenase is constructed: firstly, genes encoding the L-α-amino acid transaminase, α-hydroxycarboxylate dehydrogenase and L-glutamate dehydrogenase are ligated to a plasmid to obtain a three-gene co-expression recombinant plasmid. The plasmid is transformed into E. coli HM, and positive transformants are obtained by screening with an antibiotic plate to obtain recombinant E. coli.
After induction expression of the recombinant E. coli is completed, cells are collected, and in a reaction volume of 100 ml with cell wet weight of 40 g/L, levodopa concentration of 40 g/L, L-glutamic acid concentration of 30 g/L, and pH of 8.0, reaction is carried out at 35° C. for 12 hours. After the end of transformation, the yield and configuration of Danshensu are determined by liquid chromatography, and the results are shown in Table 7.
E.
coli HM/pETDuet-1-wcldhl-bsgdh-lct
E.
coli HM/pETDuet-1-bcldhl-bsgdh-lct
E.
coli HM/pETDuet-1-lfldhl-bsgdh-lct
E.
coli HM/pETDuet-1-efmdhd-bsgdh-lct
E.
coli HM/pETDuet-1-lpldhd-bsgdh-1-lct
E.
coli HM/pETDuet-1-lfldhd-bsgdh-lct
E.
coli HM/pETDuet-1-efmdhd-bsgdh-ect1
E.
coli HM/pETDuet-1-efmdhd-bsgdh-ect2
E.
coli HM/pETDuet-1-efmdhd-bsgdh-lpt
E.
coli HM/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HM/pRSFDuet-1-lfldhd-bsgdh-lct
E.
coli HM/pCOLADuet-1-wcldhl-bsgdh-lct
By the method described in the literature Large scale validation of an efficient CRISPR/Cas-based multi gene editing protocol in E. coli. Microbial Cell Factories,2017,16(1):68, a medium expression intensity constitutive promoter (PG) ahead of the E. coli glyceraldehyde-3-phosphate dehydrogenase gene (gpdA) is added ahead of the corresponding gene on the E. coli HM genome, and the sequence is as shown in SEQ ID NO: 8.
When expression of the gene btsT is enhanced, the E. coli HM genome is used as a template, btsT-FF/btsT-FR, btsT-gpdA-F/btsT-gpdA-R and btsT-RF/btsT-RR are used as primers, upstream sequences, promoters and downstream sequences are amplified, and btsT-FF and btsT-RR are used as primers to fuse an expression cassette containing the gpdA promoter. Then, after the expression cassette is transferred into E. coli HM together with plasmids pCasRed and pCRISPR-gDNA (containing btsT sgRNA), Cas9/sgRNA induces double-strand break at the btsT gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the btsT gene, and the gene is verified by sequencing.
When expression of the gene ybdD is enhanced, the E. coli HM genome is used as a template, ybdD-FF/ybdD-FR, ybdD-gpdA-F/ybdD-gpdA-R and ybdD-RF/ybdD-RR are used as primers, upstream sequences, promoters and downstream sequences are amplified, and ybdD-FF and ybdD-RR are used as primers to fuse an expression cassette containing the gpdA promoter. Then, after the expression cassette is transferred into E. coli HM together with plasmids pCasRed and pCRISPR-gDNA (containing ybdD sgRNA), Cas9/sgRNA induces double-strand break at the ybdD gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the ybdD gene, and the gene is verified by sequencing.
Table 8 below shows the corresponding indexes of the primer name and the sequence identity number.
According to the induction expression method described in Example 2, various types of cells are collected for transformation analysis, and the results are shown in Table 9. In the whole cell transformation system with wet cell weight of 5 g/L, pyruvic acid of 50 g/L, levodopa of 20 g/L, glucose of 50 g/L, pH of 8.0, temperature of 40° C., and shaker speed of 250 rpm, the transformation time is 12 hours.
E.
coli HM (PG-btsT)/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HM (PG-ybdD)/pCOLADuet-wcldhl-ect1-bsgdh
E.
coli HM (PG-btsT)/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HM (PG-ybdD)/pCOLADuet-1-wcldhl-ect1-bsgdh
E.
coli HM (PG-btsT, PG-ybdD)/pCOLADuet-1-lfldhd-ect1-
E.
coli HM (PG-btsT, PG-ybdD)/pCOLADuet-1-wcldhl-ect1-
E.
coli HM/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HM/pCOLADuet-1-wcldhl-ect1-bsgdh
The E. coli HM (PG-btsT, PG-ybdD) with the best effect is named E. coli HMBY.
When expression of the gene IldP is enhanced, the E. coli HM genome is used as a template, upstream sequences, promoters and downstream sequences are amplified, and an expression cassette containing the gpdA promoter is obtained. Then, after the expression cassette is transferred into E. coli HM together with plasmids pCasRed and pCRISPR-gDNA (containing IldP sgRNA), Cas9/sgRNA induces double-strand break at the IldP gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the IldP gene, and the gene is verified by sequencing.
According to the induction expression method described in Example 2, various types of cells are collected for transformation analysis, and the results are shown in Table 10. In the whole cell transformation system with wet cell weight of 5 g/L, L-lactic acid of 50 g/L, levodopa of 20 g/L, pH of 8.0, temperature of 40 C, and shaker speed of 250 rpm, the transformation time is 12 hours.
E.
coli HM (PG-lldP)/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli HM (PG-lldP)/pCOLADuet-1-wcldhl-ect1-llldh
E.
coli HM/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli HM/pCOLADuet-1-wcldhl-ect1-llldh
E. coli HM/pCOLADuet-1-wcldhl-ect1-IIldh 5.5 S>99.9 3.7
The E. coli HM (PG-IIdP) with the best effect is named E. coli HML.
When expression of the gene gltS is enhanced, the E. coli HM genome is used as a template, upstream sequences, promoters and downstream sequences are amplified, and an expression cassette containing the gpdA promoter is obtained. Then, after the expression cassette is transferred into E. coli HM together with plasmids pCasRed and pCRISPR-gDNA (containing gltS sgRNA), Cas9/sgRNA induces double-strand break at the gltS gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the gltS gene, and the gene is verified by sequencing.
According to the induction expression method described in Example 2, various types of cells are collected for transformation analysis, and the results are shown in Table 11. In the whole cell transformation system with wet cell weight of 5 g/L, L-glutamic acid of 1 g/L, levodopa of 20 g/L, pH of 8.0, temperature of 40° C., and shaker speed of 250 rpm, the transformation time is 12 hours.
E.
coli HM (PG-gltS)/pCOLADuet-1-lfldhd-
E.
coli HM (PG-gltS)/pCOLADuet-1-wcldhl-
E.
coli HM/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HM/pCOLADuet-1-wcldhl-bsgdh-lct
The E. coli HM (PG-gltS) with the best effect is named E. coli HMG.
According to the method as in Example 7, a medium expression intensity constitutive promoter (PG) ahead of the E. coli glyceraldehyde-3-phosphate dehydrogenase gene (gpdA) is added ahead of the nadA and pdxJ genes in E. coli HMBY, and the sequence is shown in SEQ ID NO: 8. The plasmid is then introduced.
When expression of the gene nadA is enhanced, the E. coli HMBY genome is used as a template, nadA-FF/nadA-FR, nadA-gpdA-F/nadA-gpdA-R and nadA-RF/nadA-RR are used as primers, upstream sequences, promoters and downstream sequences are amplified, and nadA-FF and nadA-RR are used as primers to fuse an expression cassette containing the gpdA promoter. Then, after the expression cassette is transferred into E. coli HMBY together with plasmids pCasRed and pCRISPR-gDNA (containing nadA sgRNA), Cas9/sgRNA induces double-strand break at the nadA gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the nadA gene, and the gene is verified by sequencing.
When expression of the gene pdxJ is enhanced, the E. coli HMBY genome is used as a template, pdxJ-FF/pdxJ-FR, pdxJ-gpdA-F/pdxJ-gpdA-R and pdxJ-RF/pdxJ-RR are used as primers, upstream sequences, promoters and downstream sequences are amplified, and pdxJ-FF and pdxJ-RR are used as primers to fuse an expression cassette containing the gpdA promoter. Then, after the expression cassette is transferred into E. coli HMBY together with plasmids pCasRed and pCRISPR-gDNA (containing pdxJ sgRNA), Cas9/sgRNA induces double-strand break at the pdxJ gene locus of the host, the recombinase Red integrates the gpdA promoter ahead of the pdxJ gene, and the gene is verified by sequencing.
Table 12 below shows the corresponding indexes of the primer name and the sequence identity number.
After genetic modification is completed, the co-expression plasmid is introduced. According to the induction expression method described in Example 2, various types of cells are collected for transformation and analysis, and the results are shown in Table 13. In the whole cell transformation system with cell wet weight of 20 g/L, pyruvic acid of 100 g/L, levodopa of 120 g/L, glucose of 200 g/L, pH of 9.0, temperature of 30° C., and shaker speed of 250 rpm, the transformation time is 24 hours.
E.
coli HMBY (PG-pdxJ, PG-nadA)/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HMBY (PG-pdxJ, PG-nadA)/pCOLADuet-1-wcldhl-ect1-bsgdh
E.
coli HML (PG-pdxJ)/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HMBY (PG-nadA)/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HMBY/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli HMBY/pCOLADuet-1-wcldhl-ect1-bsgdh
The E. coli HMBY(PG-nadA, PG-pdxJ) with the best effect is named E. coli NP.
After genetic modification is completed, the co-expression plasmid is introduced. According to the induction expression method as described in Example 2, various types of cells are collected for transformation and analysis, and the results are shown in Table 14. In the whole cell transformation system with wet cell weight of 20 g/L, L-lactic acid of 100 g/L, levodopa of 120 g/L, pH of 9.0, temperature of 30° C., and shaker speed of 250 rpm, the transformation time is 24 hours.
E.
coli HML (PG-pdxJ, PG-nadA)/pCOLADuet-1-lfldhd-ect1-
E.
coli HML (PG-pdxJ, PG-nadA)/pCOLADuet-1-wcldhl-ect1-
E.
coli HML (PG-pdxJ)/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli HML(PG-nadA)/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli HML/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli HML/pCOLADuet-1-wcldhl-ect1-llldh
The best-performing E. coli HML(PG-nadA,PG-pdxJ) is named E. coli NL.
After genetic modification is completed, the co-expression plasmid is introduced. According to the induction expression method described in Example 2, various types of cells are collected for transformation and analysis, and the results are shown in Table 15. In the whole cell transformation system with wet cell weight of 20 g/L, L-glutamic acid of 200 g/L, levodopa of 20 g/L, pH of 9.0, temperature of 30° C., and shaker speed of 250 rpm, the transformation time is 24 hours.
E.
coli HMG(PG-pdxJ, PG-nadA)/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HMG(PG-pdxJ, PG-nadA)/pCOLADuet-1-wcldhl-bsgdh-lct
E.
coli HMG(PG-pdxJ)/pCOLADuet-1-efmdhd-bsgdh-lct
E.
coli HMG(PG-nadA)/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HMG/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HMG/pCOLADuet-1-lfldhl-bsgdh-lct
The best-performing E. coli HMG (PG-nadA, PG-pdxJ) is named E. coli HNP.
According to the induction expression method as described in Example 2, cells are collected after induction expression of E. coli NP/pCOLADuet-1-Ifldhd-ect1-bsgdh is completed, and in a 100 ml reaction system with the wet cell weight of 1 g/L, pyruvic acid of 1 g/L, levodopa of 1 g/L, glucose of 1 g/L, pH of 6.0, temperature of 15° C. and shaker speed of 250 rpm, the transformation time is 1 hour. As a result of measurement, the concentration of R-danshensu is 77 mg/L, and e.e %>99.9.
According to the induction expression method as described in Example 2, cells are collected after induction expression of E. coli NL/pCOLADuet-1-Ifldhd-ect1-IIldh is completed, and in a 100 ml reaction system with wet cell weight of 1 g/L, L-lactic acid of 1 g/L, levodopa of 1 g/L, pH of 6.0, temperature of 15° C. and shaker speed of 250 rpm, the transformation time is 1 hour. As a result of measurement, the concentration of R-danshensu is 77 mg/L, and e.e %>99.9.
According to the induction expression method as described in Example 2, cells are collected after induction expression of E. coli HNP/pCOLADuet-1-efmdhd-bsgdh-lct is completed, and in a 100 ml reaction system with wet cell weight of 1 g/L, L-glutamic acid of 1 g/L, levodopa of 1 g/L, pH of 6.0, temperature of 15° C. and shaker speed of 250 rpm, the transformation time is 1 hour. As a result of measurement, the concentration of S-danshensu is 93 mg/L, and e.e %>99.9.
According to the induction expression method as described in Example 2, cells are collected after induction expression of the strains in Table 16 is completed, and in a 100 ml reaction system with the wet cell weight of 200 g/L, pyruvic acid of 200 g/L, levodopa of 200 g/L, glucose of 200 g/L, pH of 8.5, temperature of 40° C. and shaker speed of 250 rpm, the transformation time is 48 hours. The results are measured after the precipitate is completely diluted and dissolved.
E.
coli NP/pCOLADuet-1-lfldhd-ect1-bsgdh
E.
coli NP/pCOLADuet-1-wcldhl-ect1-bsgdh
E.
coli NP/pCOLADuet-1-lfldhd-ect1-pmaao
E.
coli NP/pCOLADuet-1-lfldhd-ect1-praao
E.
coli NP/pCOLADuet-1-wcldhl-ect1-mmaao
E.
coli NP/pCOLADuet-1-wcldhl-ect1-praao
According to the induction expression method as described in Example 2, cells are collected after induction expression of the strains in Table 17 is completed, and in a 100 ml reaction system with wet cell weight of 200 g/L, L-lactic acid of 200 g/L, levodopa of 200 g/L, pH of 8.5, temperature of 40° C. and shaker speed of 250 rpm, the transformation time is 48 hours. The results are measured after the precipitate is completely diluted and dissolved.
E.
coli NL/pCOLADuet-1-lfldhd-ect1-llldh
E.
coli NL/pCOLADuet-1-wcldhl-ect1-llldh
E.
coli NL/pCOLADuet-1-lfldhd-ect1-pmaao
E.
coli NL/pCOLADuet-1-lfldhd-ect1-praao
E.
coli NL/pCOLADuet-1-wcldhl-ect1-mmaao
E.
coli NL/pCOLADuet-1-wcldhl-ect1-praao
According to the induction expression method as described in Example 1, cells are collected after induction expression of the strains in Table 18 is completed, and in a 100 ml reaction system with wet cell weight of 200 g/L, L-glutamic acid of 20 g/L, levodopa of 200 g/L, pH of 8.5, temperature of 40° C. and shaker speed of 250 rpm, the transformation time is 48 hours. The results are measured after the precipitate is completely diluted and dissolved.
E.
coli HNP/pCOLADuet-1-lfldhd-bsgdh-lct
E.
coli HNP/pCOLADuet-1-wcldhl-bsgdh-lct
E.
coli NPP/pCOLADuet-1-lfldhd-bsgdh-ect1
E.
coli HNP/pCOLADuet-1-lfldhd-rsgdh-ect2
E.
coli HNP/pCOLADuet-1-wcldhl-csgdh-lpt
The above-mentioned enzymes and modification and construction of the co-expression genetic engineering strains thereof, the culture medium composition and culture method of the bacterial cells, and the whole cell biotransformation are only preferred examples of the present disclosure, and are not intended to limit the present disclosure. In theory, other bacteria, filamentous fungi, actinomycetes and animal cells can be genome-modified and used for multi-gene co-expression whole-cell catalysis. Any modifications and equivalent replacements made within the principles and spirit of the present disclosure fall within the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201810352649.8 | Apr 2018 | CN | national |
| 201810352693.9 | Apr 2018 | CN | national |
| 201810352695.8 | Apr 2018 | CN | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2018/111895 | Oct 2018 | US |
| Child | 16542787 | US |
