Feedback-resistant acetohydroxy acid synthase variant and method for producing L-valine using the same

Abstract

The present disclosure relates to an acetohydroxy acid synthase variant in which the feedback inhibition to L-valine is released, a polynucleotide encoding the acetohydroxy acid synthase variant, an expression vector including the polynucleotide, a microorganism producing L-valine including the acetohydroxy acid synthase variant, and a method for producing L-valine using the microorganism.

Claims

1. A polynucleotide encoding an acetohydroxy acid synthase variant in which the 137th amino acid from the N-terminus of the amino acid sequence of SEQ ID NO: 3, leucine (L), is substituted with an amino acid other than leucine, and thereby releasing the feedback inhibition to L-valine.

2. The polynucleotide of claim 1, wherein the acetohydroxy acid synthase variant has the amino acid sequence of SEQ ID NO: 4.

3. An expression vector comprising the polynucleotide of claim 1.

4. A microorganism of the genus Corynebacterium, comprising an acetohydroxy acid synthase variant in which the 137th amino acid from the N-terminus of the amino acid sequence of SEQ ID NO: 3, leucine (L), is substituted with an amino acid other than leucine, and thereby releasing the feedback inhibition to L-valine.

5. The microorganism of claim 4, wherein the acetohydroxy acid synthase variant has an amino acid sequence of SEQ ID NO: 4.

6. The microorganism of claim 4, wherein the microorganism of the genus Corynebacterium is Corynebacterium glutamicum.

7. A method for producing L-valine, comprising: (a) culturing the microorganism of claim 4 in a medium and producing L-valine; and (b) recovering L-valine from the cultured microorganism or the cultured medium.

8. A method for producing L-valine, comprising: (a) culturing the microorganism of claim 5 in a medium and producing L-valine; and (b) recovering L-valine from the cultured microorganism or the cultured medium.

9. A method for producing L-valine, comprising: (a) culturing the microorganism of claim 6 in a medium and producing L-valine; and (b) recovering L-valine from the cultured microorganism or the cultured medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Hereinafter, the present disclosure will be described in more detail with reference to the following Examples. However, these Examples are for illustrative purposes only, and the invention is not intended to be limited by these Examples.

Example 1: Selection of Mutant Strains by Artificial Mutagenesis

(2) To obtain a mutant microorganism strain having an enhanced ability to produce L-valine, the mutation of a microorganism was induced using the following method.

(3) Specifically, a parental strain, L-valine-producing Corynebacterium glutamicum Corynebacterium glutamicum KCCM11201P (Korean Patent No. 10-1117022), was inoculated into a seed medium containing the components described below, which was sterilized at 121 C. for 15 minutes, cultured for 13 hours, and 25 mL of the culture medium was recovered. The recovered cultured medium was washed with 100 mM citrate buffer and N-methyl-N-nitro-N-nitrosoguanidine (NTG) was added thereto at a final concentration of 400 g/mL, treated for 30 minutes, and the medium was washed with 100 mM phosphate buffer. The strains treated with NTG were spread on a minimal medium and the death rate was measured, and as a result, the death rate was shown to be 99.6%.

(4) To obtain a mutant strain having resistance to -aminobutyric acid (ABA), the NTG-treated strains were spread on a minimal medium containing ABA at a final concentration of 0 mM, 20 mM, 50 mM, 100 mM, and 200 mM, respectively. Then, the strains were cultured at 30 C. for 7 days to obtain an ABA-resistant mutant strain. The thus-obtained mutant strain was designated as Corynebacterium glutamicum NA100-311.

(5) <Seed Medium>

(6) Raw Sugar (20 g), Peptone (10 g), Yeast Extract (5 g), Urea (1.5 g), KH.sub.2PO.sub.4 (4 g), K.sub.2HPO.sub.4 (8 g), MgSO.sub.4.7H.sub.2O (0.5 g), Biotin (100 g), Thiamine HCl (1000 g), Calcium-Pantothenic Acid (2000 g), and Nicotinamide (2000 g) (based on 1 L of distilled water), pH 7.0

(7) <Minimal Medium>

(8) Glucose (100 g), (NH.sub.4).sub.2SO.sub.4 (40 g), Soy Protein (2.5 g), Corn Steep Solids (5 g), Urea (3 g), KH.sub.2PO.sub.4 (1 g), MgSO.sub.4.7H.sub.2O (0.5 g), Biotin (100 g), Thiamine HCl (1000 g), Calcium-Pantothenic Acid (2000 g), and Nicotinamide (3000 g) (based on 1 L of distilled water), pH 7.0

Example 2: Confirmation of the L-Valine-Producing Ability of the Selected Strain and Confirmation of the Nucleotide Sequence of ilvN

(9) To confirm the L-valine-producing ability of Corynebacterium glutamicum NA100-311, the mutant strain selected in Example 1, the strain was cultured by the following method.

(10) The parent strain (i.e., Corynebacterium glutamicum KCCM11201P) and the mutant strain (i.e., Corynebacterium glutamicum NA100-311) were inoculated in an amount of a platinum loop into 250 mL corner baffle flasks containing 25 mL of the production medium described below and cultured at 30 C. for 72 hours with shaking at 200 rpm to produce L-valine.

(11) <Production Medium>

(12) Glucose (100 g), (NH.sub.4).sub.2SO.sub.4 (40 g), Soy Protein (2.5 g), Corn Steep Solids (5 g), Urea (3 g), KH.sub.2PO.sub.4 (1 g), MgSO.sub.4.7H.sub.2O (0.5 g), Biotin (100 g), Thiamine HCl (1000 g), Calcium-Pantothenic Acid (2000 g), and Nicotinamide (3000 g) (based on 1 L of distilled water), pH 7.0

(13) Upon completion of the cultivation, the amount of L-valine production was measured by high speed liquid chromatography. The concentrations of L-valine in the culture media of the experimental strains are shown in Table 1 below.

(14) TABLE-US-00001 TABLE 1 L-Valine productivity of ABA-resistant strains L-Valine Concentration Optical Density Strain (g/L) (OD) Corynebacterium glutamicum 2.8 47.5 KCCM11201P Corynebacterium glutamicum 1.9 26.8 NA100-311

(15) According to the results above, in the case of the parent strain (i.e., Corynebacterium glutamicum KCCM11201P), the optical density of the culture was 47.5 and L-valine was produced in a concentration of 2.8 g/L, whereas, in the case of the mutant strain (i.e., Corynebacterium glutamicum NA100-311), L-valine was produced in a concentration of 1.9 g/L although the optical density of the culture was only 26.9. Upon calculation of the concentration of L-valine (g/L/OD) produced per optical density 1, the concentration of L-valine for the parent strain (i.e., Corynebacterium glutamicum KCCM11201P) was shown to be 0.059 while the mutant strain (i.e., Corynebacterium glutamicum NA100-311) showed an increased value of 0.071, thus suggesting that the amount of L-valine produced by the same amount of cells in the mutant strain was increased by 20.3% compared to that of the parent strain.

(16) To confirm the nucleotide sequence of the ilvN gene, which encodes the small subunit of acetohydroxy acid synthase in the mutant strain (i.e., Corynebacterium glutamicum NA100-311), the chromosomal DNA of the mutant strain was amplified by polymerase chain reaction (hereinafter, PCR).

(17) Specifically, first, an about 950 bp fragment was amplified using the chromosomal DNA of the mutant strain (i.e., Corynebacterium glutamicum NA100-311) as a template along with the primers of SEQ ID NOS: 1 and 2, under the following conditions: 28 cycles of denaturation at 94 C. for 1 min, annealing at 58 C. for 30 sec, and polymerization at 72 C. for 40 sec using Taq DNA polymerase. Upon analysis of the nucleotide sequence using the primers, it was confirmed that the 409.sup.th nucleotide, C, was substituted with T and this suggests that the mutation was the substitution of the 137.sup.th amino acid, leucine, with phenylalanine.

Example 3: Preparation of a Vector Including a Substituted Nucleotide Sequence of ilvN

(18) To prepare a vector including the mutated nucleotide sequence confirmed in Example 2, an about 1726 bp fragment having BamHI and XbaI restriction sites was amplified using the chromosomal DNA of the mutant strain as a template along with the primers of SEQ ID NOS: 1 and 2, under the following conditions: 25 cycles of denaturation at 94 C. for 1 min, annealing at 58 C. for 30 sec, and polymerization at 72 C. for 1 min using Pfu DNA polymerase. The amplified fragment was treated with restriction enzymes, BamHI and XbaI, and ligated into a pDZ, which was treated with the same restriction enzymes, to prepare pDZ-ilvN(L137F).

Example 4: Preparation of a Strain where a Nucleotide Sequence of ilvN is Substituted

(19) To prepare a strain which includes the ilvN-mutated nucleotide sequence discovered in the above mutant strain, Corynebacterium glutamicum KCCM11201P, which produces L-valine, was used as the parent strain.

(20) The Corynebacterium glutamicum KCCM11201P was transformed with the pDZ-ilvN(L137F) vector prepared in Example 3 by electroporation. An L-valine-producing strain, in which the 137.sup.th amino acid, leucine, was substituted with phenylalanine, in an amino acid sequence encoded by ilvN gene on the chromosome of Corynebacterium glutamicum KCCM11201P, was obtained by second crossover. The presence of the substitution of ilvN was confirmed by analyzing a 1726 bp fragment with the primer of SEQ ID NO: 2, after amplifying the 1726 bp fragment by PCR using the primers of SEQ ID NOS: 1 and 2 under the following conditions: 28 cycles of denaturation at 94 C. for 1 min, annealing at 58 C. for 30 sec, and polymerization at 72 C. for 40 sec using Taq DNA polymerase.

(21) The strain transformed with the pDZ-ilvN(L137F) vector was named as Corynebacterium glutamicum KCJ-644 and deposited at the Korean Culture Center of Microorganisms (KCCM), having an address of Purim BID, 45, Hongjenae-2ga-gil, Seodaemun-gu, Seoul 120-861, Republic of Korea, which is recognized as an international depositary authority under the Budapest Treaty, on Nov. 22, 2013, under the accession number KCCM11485P.

Example 5: Production of L-Valine in a Strain where a Nucleotide Sequence of ilvN is Substituted

(22) To produce L-valine from the Corynebacterium glutamicum KCJ-644, the L-valine-producing strain prepared in Example 4, the strain was cultured by the following method.

(23) The parent strain (i.e., Corynebacterium glutamicum KCCM11201P) and the Corynebacterium glutamicum KCJ-644 prepared above were inoculated in an amount of a platinum loop into 250 mL corner baffle flasks containing 25 mL of the production medium and cultured at 30 C. for 72 hours with shaking at 200 rpm to produce L-valine.

(24) Upon completion of the cultivation, the amount of L-valine production was measured by high speed liquid chromatography. The concentrations of L-valine in the culture media of the experimental strains are shown in Table 2 below.

(25) TABLE-US-00002 TABLE 2 L-Valine productivity of Corynebacterium glutamicum KCCM11201P and Corynebacterium glutamicum KCJ-644 Strain L-Valine Concentration (g/L) Corynebacterium glutamicum 2.8 KCCM11201P Corynebacterium glutamicum 3.0 KCJ-644

(26) As shown in Table 2, the Corynebacterium glutamicum KCJ-644, which is an L-valine-producing strain having an L137F mutation on the ilvN gene, showed a 7.1% increase in L-valine productivity, compared to the parent strain, i.e., Corynebacterium glutamicum KCCM11201P.

Example 6: Measurement of Acetohydroxy Acid Synthase Activity in a Strain where a Nucleotide Sequence of ilvN is Substituted

(27) To measure the acetohydroxy acid synthase activity in the Corynebacterium glutamicum KCJ-644, which is an L-valine-producing strain prepared in Example 4, an experiment was performed by the following method.

(28) The parent strain (i.e., Corynebacterium glutamicum KCCM11201P) and the Corynebacterium glutamicum KCJ-644 prepared above were inoculated in an amount of a platinum loop into 250 mL corner baffle flasks containing 25 mL of the seed medium and cultured at 30 C. for 16 hours with shaking at 200 rpm. Upon completion of the cultivation, the culture medium was centrifuged and the supernatant was discarded, and the pellet was washed and mixed with a lysis buffer and the cells were pulverized with a bead homogenizer. The proteins present in the lysate were quantitated according to the Bradford assay, and the activity of acetohydroxy acid synthase was measured by measuring the acetoin produced when the lysate containing 100 g/mL of proteins was used. The measurement results of the acetohydroxy acid synthase activity in each strain are shown in Table 3 below.

(29) TABLE-US-00003 TABLE 3 Strain ilvN Activity (M/mg/min) Corynebacterium glutamicum 73.6 KCCM11201P Corynebacterium glutamicum 84.1 KCJ-644

(30) As shown in Table 3, the Corynebacterium glutamicum KCJ-644, which is an L-valine-producing strain having an L137F mutation on the ilvN gene, showed a 14.3% increase in L-valine productivity, compared to the parent strain, i.e., Corynebacterium glutamicum KCCM11201P.

(31) From the foregoing, a skilled person in the art to which the present disclosure pertains will be able to understand that the present disclosure may be embodied in other specific forms without modifying the technical concepts or essential characteristics of the present disclosure. In this regard, the exemplary embodiments disclosed herein are only for illustrative purposes and should not be construed as limiting the scope of the present disclosure. On the contrary, the present disclosure is intended to cover not only the exemplary embodiments but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the present disclosure as defined by the appended claims.