阅读说明：本技术 促进普鲁兰酶胞外表达的信号肽 (Signal peptide for promoting pullulanase extracellular expression ) 是由 佟毅 刘松 徐奎栋 李江华 陈坚 于 2020-07-30 设计创作，主要内容包括：本发明公开了促进普鲁兰酶胞外表达的信号肽,属于基因工程及酶工程技术领域。本发明是以枯草芽孢杆菌(Bacillus subtilis)表达宿主,通过对枯草芽孢杆菌内源信号肽AprE、SacB、Epr进行同义突变,得到能使胞外蛋白量显著提高的同义突变序列,在保证蛋白正常翻译的同时,又能提高蛋白的表达量。Apre、Epr、SacB信号肽的同义突变序列分别能使胞外酶活较野生型提高2.92,1.08,1.37倍,从而为普鲁兰酶的胞外高效表达提供一种策略。(The invention discloses a signal peptide for promoting the extracellular expression of pullulanase, belonging to the technical field of genetic engineering and enzyme engineering. According to the invention, a Bacillus subtilis expression host is used, and a synonymous mutation sequence capable of obviously improving the extracellular protein amount is obtained by performing synonymous mutation on Bacillus subtilis endogenous signal peptides AprE, SacB and Epr, so that the normal translation of the protein is ensured, and the expression amount of the protein can be improved. The synonymous mutation sequences of the Apre, Epr and SacB signal peptides can respectively improve the extracellular enzyme activity by 2.92, 1.08 and 1.37 times compared with the wild type, thereby providing a strategy for the extracellular high-efficiency expression of the pullulanase.)

1. The signal peptide is characterized in that the nucleotide sequences of the signal peptide are respectively shown as SEQ ID NO.1, SEQ ID NO.2 and SEQ ID NO. 3.

2. A recombinant plasmid comprising the signal peptide of claim 1.

3. A recombinant bacterium comprising the signal peptide according to claim 1 or the recombinant plasmid according to claim 2.

4. A method for increasing the expression level of a protein, comprising producing the protein using the recombinant strain of claim 3 as a fermentation strain.

5. The method according to claim 4, wherein the recombinant bacterium is cultured and OD is obtained₆₀₀At least 3 bacterial liquid, and inoculating the bacterial liquid into the reaction system in an amount of 1-10 mL/100 mL.

6. A method for increasing the expression level of extracellular proteins of Bacillus subtilis, which comprises adding the signal peptide of claim 1 to the N-terminus of the nucleotide sequence encoding the protein.

7. The method according to claim 6, characterized in that the method is: adding the signal peptide of claim 1 to the N-terminal of a target protein to construct a recombinant plasmid; and introducing the recombinant plasmid into bacillus subtilis to construct a recombinant bacterium.

8. The method of claim 6, wherein the protein of interest comprises pullulanase and/or sfGFP.

9. The method according to claim 7, wherein the pullulanase has NCBI accession No. AMQ 67157; the nucleotide sequence for coding the sfGFP is shown as SEQ ID NO. 7.

10. Use of the signal peptide according to claim 1, or the recombinant plasmid according to claim 2, or the recombinant bacterium according to claim 3, or the method according to any one of claims 4 to 9 for increasing the expression level of extracellular proteins.

Technical Field

The invention relates to a signal peptide for promoting the extracellular expression of pullulanase, belonging to the technical field of genetic engineering and enzyme engineering.

Background

Pullulanase (EC 3.2.1.41) belongs to the family of alpha-amylases, and is capable of specifically hydrolyzing the branched alpha-1, 6-glucosidic bonds of amylopectin, also known as starch debranching enzyme. However, when wild strains are used as production strains to produce pullulanase, various problems exist, including difficult culture, low yield and the like, so that the industrial large-scale production is difficult to realize. With the rapid development of genetic engineering, the pullulanase coding gene realizes heterologous expression in different genetic engineering strains.

Soluble expression of pullulanase in B.subtilis has been successfully achieved in our earlier studies, and expression of pullulanase has been driven by a strong promoter, PlyTR (Yang, S et al, mutagenesis and administration of endogenous end phase-dependent microorganisms in Bacillus subtilis, 2017). However, although the extracellular enzyme activity of pullulanase has been significantly improved by these means, it still meets the requirement of large-scale industrial production. Therefore, how to further increase the extracellular expression level of pullulanase is still a problem to be solved.

Disclosure of Invention

In order to solve the problems, the extracellular expression of the pullulanase is further improved, and the extracellular expression of the pullulanase can be improved by means of synonymous mutation. Synonymous mutations in a gene may leave the amino acid sequence unchanged, but may result in significant changes in the level of gene transcription. The N-terminal coding region of the gene is modified by a synonymous mutation means, so that the gene expression level can be remarkably improved, and the influence on the enzyme activity can be almost ignored. According to the invention, the extracellular enzyme activity of the pullulanase can be obviously improved by using the signal peptide screened by the synonymous mutation.

The invention provides a signal peptide, wherein the nucleotide sequence of the signal peptide is shown in any one of SEQ ID No. 1-3.

In one embodiment of the invention, the nucleotide sequence of the signal peptide is the signal peptide AprE, SacB, Epr synonymous mutant sequence, respectively.

In one embodiment of the invention, the synonymous mutant sequence of the signal peptide AprE is shown as SEQ ID No. 1; the synonymous mutation sequence of the signal peptide SacB is shown as SEQ ID NO. 2; the synonymous mutant sequence of the signal peptide Epr is shown as SEQ ID NO. 3.

The invention provides a recombinant plasmid containing a signal peptide with a nucleotide sequence shown as SEQ ID No. 1-3.

In one embodiment of the present invention, the heavy plasmid is any vector that can be expressed in Bacillus subtilis.

In one embodiment of the invention, the starting vector comprises P43 NMK.

In one embodiment of the present invention, the recombinant plasmid further comprises a constitutive promoter.

In one embodiment of the invention, the constitutive promoter comprises a LytR promoter, and the nucleotide sequence of the LytR promoter is shown in SEQ ID No. 4.

The invention provides a recombinant bacterium containing a signal peptide with a nucleotide sequence shown as SEQ ID No. 1-3.

In one embodiment of the present invention, the recombinant bacterium is a bacillus subtilis host.

In one embodiment of the present invention, the recombinant bacterium is a host bacillus subtilis WB600 or bacillus subtilis 168.

The invention provides a method for improving protein expression quantity, which takes a recombinant strain containing a signal peptide with a nucleotide sequence shown as SEQ ID No. 1-3 as a fermentation strain to produce protein.

In one embodiment of the present invention, the recombinant bacterium is cultured to OD₆₀₀And (3) inoculating the bacterial liquid not lower than 3.0 into the reaction system according to the proportion of 1-10 mL/100 mL.

In one embodiment of the present invention, the culture medium of the culture system is TB culture medium, and the TB culture medium is cultured at 30-40 ℃ and 200-250 rpm for 25-35 hours.

The invention provides a method for improving the extracellular protein expression quantity of bacillus subtilis, which adds a signal peptide with a nucleotide sequence shown as SEQ ID NO. 1-3 at the N end of a nucleotide sequence of a coded protein.

In one embodiment of the invention, a signal peptide with a nucleotide sequence shown in SEQ ID No. 1-3 is added to the N-terminal of a target protein, a recombinant plasmid is constructed, and the recombinant plasmid is introduced into Bacillus subtilis.

In one embodiment of the present invention, a signal peptide having a nucleotide sequence represented by SEQ ID NO.1 to 3 is inserted after the initiation codon ATG of a nucleotide sequence encoding a target protein.

In one embodiment of the invention, the protein of interest is any protein that can be expressed extracellularly in B.subtilis.

In one embodiment of the invention, the protein of interest comprises pullulanase and/or sfGFP.

In one embodiment of the invention, the amino acid sequence of pullulanase has NCBI accession number AMQ67157 and the amino acid sequence is shown in SEQ ID NO. 5.

In one embodiment of the invention, the nucleotide sequence encoding sfGFP is shown in SEQ ID No. 7.

The invention also protects the application of the signal peptide with the nucleotide sequence shown in SEQ ID NO. 1-3, or the recombinant plasmid containing the signal peptide with the nucleotide sequence shown in SEQ ID NO. 1-3, or the recombinant bacterium containing the signal peptide with the nucleotide sequence shown in SEQ ID NO. 1-3 in improving the expression quantity of extracellular proteins.

The invention also protects the application of the method for improving the protein expression quantity in improving the extracellular protein expression quantity.

The invention also protects the application of the method for improving the extracellular protein expression quantity of the bacillus subtilis in improving the extracellular protein expression quantity.

The invention also protects the application of the recombinant plasmid, the recombinant bacterium or the synonymous mutant sequence of the signal peptides AprE, SacB and Epr in improving the expression quantity of extracellular proteins.

The invention has the beneficial effects that:

the signal peptides AprE, SacB and Epr are subjected to synonymous mutation, so that a synonymous mutation sequence capable of improving the extracellular expression of the protein is screened out, the obtained mutation sequence is fused at the N end of the pullulanase, the extracellular enzyme activity yield of the pullulanase can be obviously improved and reduced, and the extracellular enzyme activity of the pullulanase is respectively improved by 2.92, 1.08 and 1.37 times in the conversion production of bacillus subtilis.

Drawings

FIG. 1 shows the expression plasmid maps of the fusion of signal peptide and sfGFP to the N-terminal and C-terminal of pullulanase, respectively (AprE is taken as an example).

FIG. 2 is a map of an expression plasmid in which a signal peptide is fused to the N-terminus of pullulanase (AprE is taken as an example).

FIG. 3 shows the extracellular enzyme activities of pullulanase secreted by wild-type and NCS-modified strains.

Detailed Description

Seed culture medium: 10g/L of peptone, 5g/L of yeast extract and 5g/L of sodium chloride.

The fermentation medium is TB medium: peptone 12g/L, yeast extract 24g/L, glycerin 4mL/L, KH₂PO₄0.017mol/L，K₂HPO₄0.072mol/L。

Seed culture: and (3) selecting a single colony of the engineering bacteria, inoculating the single colony of the engineering bacteria into a triangular flask (250mL) with the liquid loading capacity of 25mL, culturing at the temperature of 37 ℃, and culturing for 12 hours at the rotating speed of a shaking table of 200 r/min.

Fermentation culture: the mixture was inoculated into a 25mL Erlenmeyer flask (250mL) at an inoculum size of 4% (v/v), and the fermentation was carried out at 37 ℃ for 48 hours.

And (3) measuring the green fluorescent protein expression level and biomass: in a 96-well plate, if 200. mu.L of the diluted fermentation broth was used, a Cytation3 cell imaging microplate detector (Berton instruments, Inc. USA) was used, and the green fluorescence excitation wavelength: 480nm, green fluorescence emission wavelength: 520nm, cell growth OD absorption wavelength: 600 nm.

The pullulanase enzyme activity determination method comprises the following steps: 1mL of 1mg/100mL pullulan polysaccharide substrate and 0.9mL of 100mM acetic acid-sodium acetate buffer solution with pH4.5 are uniformly mixed, the mixture is placed in a water bath kettle at 60 ℃ for preheating for 10min, 0.1mL of pullulanase solution is added, after the reaction is carried out for 10min, 3mL of DNS color developing solution is added, then the mixture is boiled in a boiling water bath for 7min, the mixture is placed in ice water to stop the color developing reaction, 10mL of deionized water is added, the mixture is uniformly mixed, and the light absorption value is measured at 540 nm.

Definition of enzyme activity: the amount of enzyme that produces 1. mu. mol of reducing sugar per unit time is one unit of enzyme activity.