Patent Publication Number: US-2023143972-A1

Title: Nadph-regeneration system based on monomeric isocitrate dehydrogenase and use thereof

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. Non-Provisional patent application Ser. No. 17/189,143, entitled “NADPH-REGENERATION SYSTEM BASED ON MONOMERIC ISOCITRATE DEHYDROGENASE AND USE THEREOF,” and filed on Mar. 1, 2021. U.S. Non-Provisional patent application Ser. No. 17/189,143 claims priority to Korean Patent Application No. 10-2021-0023232 filed on Feb. 22, 2021. The entire contents of each of the above-listed applications are hereby incorporated by reference for all purposes. 
    
    
     SEQUENCE LISTING 
     The instant application contains a Sequence Listing which has been filed electronically in XML format and is hereby incorporated by reference in its entirety. Said XML copy, created on Nov. 10, 2022, is named Sequence_Listing_PLS21306DIV1ST26.xml and is 17 KB in size. 
     TECHNICAL FIELD 
     The following disclosure relates to an NADPH-regeneration system based on monomeric isocitrate dehydrogenase (IDH) and a use thereof, and in particular, to an NADPH-regeneration system based on isocitrate dehydrogenase in a monomeric form, for the regeneration of NADPH, which is a cofactor used in an enzymatic reaction of an NADPH-dependent enzyme, and an application method thereof. 
     BACKGROUND 
     NADPH-dependent enzymes, for example, cytochrome P450, are a group of enzymes found in most species that function as monooxygenases. 
     Cytochrome P450 enzymes can mediate an oxidation reaction of a wide range of substrates, and thus, can be applied to various biosynthetic and/or degradative pathways. Cytochrome P450 enzymes not only produce high value-added biological compounds, thereby having great potential in a field of drug metabolism, but also has a very high utility value as an enzyme in industrial processes. In addition, cytochrome P450 enzymes perform an important oxidation reaction in metabolic processes of drugs or hormones, etc. in vivo, and are responsible for metabolism of greater than or equal to 75% of drugs administered to humans. Furthermore, cytochrome P450 enzymes are able to control functionality of various substrates by participating in hydroxylation reactions of the various substrates, and thus, may be widely used in the discovery of optimal metabolites or high value-added processes. 
     Since cytochrome P450s, especially in eukaryotes, exist typically as a membrane protein, expression and purification in foreign hosts are difficult. In addition, since most cytochrome p450s need to receive electrons from reductase, they need nicotinamide adenine dinucleotide phosphate reduced form (NADPH) as an electron transfer material. However, NADPH, which is a cofactor used in the enzymatic reaction, is highly unstable and very expensive, and there are thus may restrictions on the industrial use of cytochrome P450s. 
     Meanwhile, cytochrome P450 BM3, which is a cytochrome P450 from  Bacillus megaterium , unlike other cytochrome P450s, has an oxygenase domain involved in enzyme activity and a reductase domain that provides a reducing power required for enzyme activity through oxidation of the cofactor are not only expressed in a form of a monocistronic protein, but also expressed in cytoplasm, such that expression and purification are relatively easy. In addition, although cytochrome P450 BM3 is a multidomain protein of about 119 kDa in size, it is characterized in that a soluble overexpression in  Escherichia coli  is possible. Thus, in order to utilize cytochrome P450 BM3 as an enzyme for the industrial processes, a lot of studies for improving substrate specificity and enzyme activity, etc., are being actively conducted. 
     However, since NADPH, which is the cofactor of cytochrome P450, is unstable and very expensive, as described above, there is still a limitation in industrial use. In order to solve the above problems, various NADPH-regeneration systems have been developed. Specifically, the NADPH-regeneration system may use electrochemical, optical, and enzymatic methods, of which an enzymatic method is mainly used. 
     Examples of enzymes used in an enzyme-mediated NADPH-regeneration system include enzymes that produce NADPH in metabolic pathways in-vivo such as alcohol dehydrogenase (ADH), formate dehydrogenase (FDH), glucose dehydrogenase (GDH), and glucose 6-phosphate dehydrogenase (G6PDH). 
     However, all of the enzymes currently used in the NADPH-regeneration system are in a multimeric form, and have difficulties with soluble expression in  E. coli . In particular, structural characteristics of the multimeric form have a negative influence on the enzymatic reaction, soluble expression, and upon expression of fusion protein of the NADPH-dependent enzyme such as cytochrome P450 and an enzyme used in the NADPH-regeneration system, and thus, act as a serious limiting factor in the case of producing a high value-added substance through an enzymatic process or a whole-cell reaction. 
     Thus, there is a need in the art for an NADPH-regeneration system capable of stably supplying NADPH to the enzymatic reaction in which the NADPH-dependent enzyme acts as a catalyst. Thus, in order to solve the problem of an enzyme used in the NADPH-regeneration system of the prior art, there is an urgent need to find an enzyme that may be used in the NADPH-regeneration system in a monomeric form, is capable of the soluble overexpression in  E. coli , and is capable of a fusion expression with the NADPH-dependent enzyme. 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         Korean Patent Publication No. 2022137 
         Korean Patent Publication No. 1152878 
       
    
     Non-Patent Document 
     
         
         Xiaodong Wang et al., Chem., 2(5) pp. 621-654 (2017) 
       
    
     SUMMARY 
     In order to solve the problem of expensive cofactor and cofactor regeneration, which determines productivity or price of a product, in a process of developing a biocatalytic process with useful activity dependent on a cofactor using enzymes or whole-cells, an embodiment of the present disclosure is directed to providing an isocitrate dehydrogenase recombinant protein from  Corynebacterium glutamicum  and an isocitrate dehydrogenase recombinant protein from  Azotobacter vinelandii  that are solubly expressed in  E. coli  in a monomeric form and may be used in an NADPH-regeneration system, and a novel NADPH-regeneration system using the same. 
     In one general aspect, there is provided a recombinant expression vector for NADPH regeneration, including a polynucleotide encoding monomeric isocitrate dehydrogenase from  Corynebacterium glutamicum  or  Azotobacter vinelandii . The recombinant expression vector may further include a polynucleotide encoding an NADPH-dependent enzyme. 
     The isocitrate dehydrogenase from  Corynebacterium glutamicum  may consist of an amino acid sequence of SEQ ID NO: 1 and the isocitrate dehydrogenase from  Azotobacter vinelandii  may consist of an amino acid sequence of SEQ ID NO: 2. 
     The NADPH-dependent enzyme may be any one or two or more selected from the group consisting of dehydrogenase, reductase, oxidoreductase, transhydrogenase, peroxidase, oxygenase, monooxygenase, flavodoxin, and dehalogenase. The NADPH-dependent enzyme may be recombined and fused to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 2, or may be linked by addition of a chemical linker. 
     The chemical linker may be selected from the group consisting of PEGylated bis(sulfosuccinimidyl) suberate (BS(PEG)5), PEGylated bis(sulfosuccinimidyl) suberate (BS(PEG)9), bis(sulfosuccinimidyl) glutarate-d0 (BS2G-d0), bis(sulfosuccinimidyl) 2,2,4,4-glutarate-d4 (BS2G-d4), di succinimidyl dibutyric urea (DSBU), 1,5-difluoro-2,4-dinitrobenzene (DFDNB), dimethyl pimelimidate (DMP), dimethyl suberimidate (DMS), disuccinimidyl glutarate (DSG), dithiobis(succinimidyl) propionate (DSP), di succinimidyl suberate (DSS), disuccinimidyl sulfoxide (DSSO), disuccinimidyl tartarate (DST), dimethyl-3,3-dithiobis propionimidate (DTBP), ethylene glycol bis(succinimidyl) succinate (EGS), tris-(succinimidyl) aminotriacetate (T SAT), and 1-ethyl-3-(3-dim ethyl aminopropyl) carbodiimide (EDC). 
     The present invention provides a transformant transformed with the recombinant expression vector for NADPH regeneration. The transformant may be  Escherichia coli.    
     In another general aspect, there is provided a method for producing a recombinant protein including: producing the recombinant expression vector for NADPH regeneration as described above; transforming the recombinant expression vector to produce a transformant; culturing the transformant to overexpress isocitrate dehydrogenase from  Corynebacterium glutamicum  or isocitrate dehydrogenase from  Azotobacter vinelandii ; and recovering the overexpressed recombinant protein. The culturing may be performed at 28 to 32° C. 
     The present invention provides a recombinant protein produced by the method for producing a recombinant protein. The recombinant protein may be solubly expressed in a monomeric form, and may be used together with the NADPH-dependent enzyme. The NADPH-dependent enzyme may be any one or two or more selected from the group consisting of dehydrogenase, reductase, oxidoreductase, transhydrogenase, peroxidase, oxygenase, monooxygenase, flavodoxin, and dehalogenase. The NADPH-dependent enzyme may be recombined and fused to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 2, or may be linked by addition of a chemical linker. 
     The chemical linker may be selected from the group consisting of BS(PEG)5, BS(PEG)9, BS2G-d0, BS2G-d4, DSBU, DFDNB, DMP, DMS, DSG, DSP, DSS, DSSO, DST, DTBP, EGS, TSAT, and EDC. 
     The present invention provides a composition for NADPH regeneration, comprising the recombinant protein. 
     The present invention provides a method for regenerating NADPH including: regenerating NADPH by adding the recombinant protein to an NADPH-dependent enzyme reaction system. 
     The present invention provides a kit for NADPH regeneration, including the recombinant protein. 
     In another general aspect, there is provided a composition for substrate hydroxylation, comprising the recombinant protein; and a cytochrome P450 protein. The substrate may be selected from the group consisting of omeprazole, omeprazole sulfide, ethoxycoumarin, and nitrophenol. 
     The present invention provides an in vitro toxicity test method including: treating the composition for substrate hydroxylation. 
     The present invention provides a method for converting a target substrate by co-expressing or fusion expressing the recombinant isocitrate dehydrogenase protein and the NADPH-dependent enzyme. 
     Other features and aspects will be apparent from the following detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a schematic diagram illustrating an NADPH-regeneration system based on isocitrate dehydrogenase in a monomeric form according to the present invention; 
         FIGS.  2 A and  2 B  illustrate schematic diagrams of the recombinant vector for expressing a recombinant protein of isocitrate dehydrogenase from  Corynebacterium glutamicum  (hereinafter may be referred to as CgIDH) and a recombinant protein of isocitrate dehydrogenase from  Azotobacter vinelandii  (hereinafter may be referred to as AvIDH); 
         FIGS.  3 A and  3 B  are each a SDS-PAGE analysis result depending on an expression temperature of CgIDH and AvIDH; 
         FIGS.  4 A and  4 B  are each a SDS-PAGE analysis result that can confirm a pure separation and purification result of CgIDH and AvIDH; 
         FIG.  5    is a size-exclusion chromatography analysis result of CgIDH and AvIDH; 
         FIGS.  6 A and  6 B  are an analysis result of the kinetic constants (Km and Vmax) of CgIDH and AvIDH; 
         FIG.  7    is a measurement result of an enzyme activity of CgIDH and AvIDH; 
         FIGS.  8 A and  8 B  are graphs of results obtained by performing a coupling reaction between CgIDH or AvIDH and cytochrome P450 BM3, which is the NADPH-dependent enzyme, and performing an analysis with a spectrophotometer; 
         FIGS.  9 A and  9 B  are graphs showing the degree of increase of NAPDH when determining an optimal enzyme concentration ratio for a coupling reaction between CgIDH or AvIDH and cytochrome P450 BM3; 
         FIGS.  10 A- 10 F  are a series of HPLC analysis results of a hydroxylation reaction of a substrate by the coupling reaction between CgIDH or AvIDH and cytochrome P450 BM3; 
         FIG.  11    is storage stability evaluation results of CgIDH and AvIDH; 
         FIG.  12    is an evaluation result of an enzyme activity inhibitory effect by α-ketoglutarate, which is a reaction product of CgIDH and AvIDH recombinant proteins. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an NADPH-regeneration system based on monomeric isocitrate dehydrogenase of the present invention and a use thereof will be described in detail with reference to the accompanying table or drawings. 
     If the drawings are described, they are provided as examples so that the spirit of the present invention can be sufficiently transferred to those skilled in the art. Therefore, the present invention is not limited to the accompanying drawings, but may be modified in many different forms. In addition, the accompanying drawings described below will be exaggerated in order to illustrate the spirit and scope of the present invention. 
     Terms such as “first”, “second”, etc. may be used to describe various components, but these components are not to be construed as being limited to these terms. The terms are used only to distinguish one component from another component. For example, a first component may be referred to as a second component and the second component may also be similarly referred to as the first component, without departing from the scope of the present invention. 
     Technical terms and scientific terms used in the present specification have the general meaning understood by those skilled in the art to which the present invention pertains unless otherwise defined, and a description for the known function and configuration unnecessarily obscuring the gist of the present invention will be omitted in the following description and the accompanying drawings. Terms generally used and defined by a dictionary should be interpreted as having the same meanings as meanings within a context of the related art and should not be interpreted as having ideal or excessively formal meanings unless being clearly defined otherwise in the present specification. 
     In addition, singular forms used in the specification of the present invention are intended to include the plural forms as well unless otherwise indicated in context. 
     Further, units used in the specification of the present invention without special mention are by weight, and as an example, the unit of % or ratio means % by weight or a ratio by weight, respectively. 
     Furthermore, in the specification of the present invention, the expression “comprise” is an “open” description having the meaning equivalent to expressions such as “include,” “contain,” “have,” or “feature”, and does not exclude elements, materials, or processes that are not further listed. In addition, the expression “substantially composed of . . . ” means that other elements, materials, or processes not listed with the specified element, material or process may be present in an amount that does not have an unacceptably significant effect on at least one basic and novel technical idea of the invention. Further, the expression “composed of” means that only the described elements, materials, or processes are present. 
     In the specification of the present invention, “NADPH regeneration” is meant to include not only a process of recycling NADPH together with an NADPH-dependent enzyme by converting NADP +  produced by the NADPH-dependent enzyme into NADPH, but also a reaction of producing NADPH from free NADP + , as can be seen in  FIG.  1   , unless otherwise specified. 
     In the specification of the present invention, the term “vector”, “expression vector”, or “recombinant expression vector” is a linear or circular DNA molecule that encodes an operably linked polynucleotide, comprising elements and additional fragments that provide for gene transcription and translation. Additional fragments include a promoter, a transcription termination sequence, etc. A vector, an expression vector, or a recombinant expression vector includes one or more origins replication, one or more selection markers, etc. A vector, an expression vector, or a recombinant expression vector is generally derived from plasmid or viral DNA, or contains elements of both of them. 
     In the specification of the present invention, the term “recombination protein” refers to a conventional expression protein that expresses a gene from a cell of another species using a heterologous host, but includes a protein to which another protein is linked or a different amino acid sequence is added to an amino or carboxyl terminus of a target protein sequence, if necessary. In the present invention, an affinity tag may be further included at the carboxyl terminus of a recombinant protein of isocitrate dehydrogenase from  Corynebacterium glutamicumr  (CgIDH) and a recombinant protein of isocitrate dehydrogenase from  Azotobacter vinelandii  (AvIDH) for ease of purification. A histidine tag (his-tag) may be used as the affinity tag, but is not limited thereto. 
     A recombinant expression vector for NADPH regeneration according to the present invention includes a polynucleotide encoding an isocitrate dehydrogenase recombinant protein (CgIDH or AvIDH) monomer from  Corynebacterium glutamicum  or  Azotobacter vinelandii . Here, the recombinant expression vector may preferably be one such that the recombinant protein monomer is solubly overexpressed, but is not limited thereto. 
     The isocitrate dehydrogenase from  Corynebacterium glutamicum , as a specific example, may consist of an amino acid sequence of SEQ ID NO: 1 and the isocitrate dehydrogenase from  Azotobacter vinelandii  may consist of an amino acid sequence of SEQ ID NO: 2. 
     The polynucleotide is not particularly limited as long as it is a nucleic acid sequence capable of encoding CgIDH or AvIDH. For example, the polynucleotide encoding CgIDH may consist of, but is not limited to, a nucleic acid sequence of SEQ ID NO: 7, and the polynucleotide encoding AvIDH may consist of a nucleic acid sequence of SEQ ID NO: 8. The polynucleotide may be operably linked to the promoter to ensure that the expression of the protein is well achieved when introduced into a recombinant expression vector. 
     Here, the term “operably linked” refers to a state in which a nucleic acid expression control sequence and a nucleic acid sequence encoding a target protein or RNA are functionally linked to perform a general function. For example, the nucleic acid sequence encoding the protein or RNA is operably linked with the promoter, which can affect the expression of the coding sequence. An operable linkage with the expression vector may be produced by gene recombination techniques well known in the art, and site-specific DNA cleavage and linkage may be used by appropriately introducing enzymes or homologous gene recombination techniques, etc. generally known in the art. 
     The promoter may be derived from, but is not limited to, a subject (host) to which a recombinant vector of the present invention is to be introduced, and examples of thereof include a T7 promoter. 
     In the transformant into which the recombinant vector was introduced, CgIDH and/or AvIDH are/is expressed from the polynucleotide encoding CgIDH and/or the polynucleotide encoding AvIDH. 
     The recombinant vector of the present invention may be, but is not limited to, a plasmid vector, a cosmid vector, a bacteriophage vector, a viral vector, etc. as template. A preferred example thereof may include a promoter, an operator, an initiation codon, a stop codon, an expression control element such as a polyadenylation signal and an enhancer, etc., and may be prepared in various ways according to the purpose. The recombinant vector may include an antibiotic resistance marker for selection of transformants into which the vector was introduced, which may be inherent in the vector or may be introduced from the outside. 
     In the recombinant expression vector for NADPH regeneration according to an embodiment of the present invention, the recombinant expression vector may further include a polynucleotide encoding the NADPH-dependent enzyme. A specific example of the NADPH-dependent enzyme may be, but is not limited to, any one or two or more selected from the group consisting of dehydrogenase, reductase, oxidoreductase, transhydrogenase, peroxidase, oxygenase, monooxygenase, flavodoxin, and dehalogenase, preferably dehydrogenase. 
     In the recombinant expression vector for NADPH regeneration according to an embodiment of the present invention, the NADPH-dependent enzyme may be recombined and fused to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 2, or may be linked by addition of a chemical linker. 
     In the recombinant expression vector for NADPH regeneration according to an embodiment of the present invention, the chemical linker may be selected from the group consisting of BS(PEG)5, BS(PEG)9, BS2G-d0, BS2G-d4, DSBU, DFDNB, DMP, DMS, DSG, DSP, DSS, DSSO, DST, DTBP, EGS, TSAT, and EDC. 
     The present invention provides a transformant transformed with the recombinant expression vector for NADPH regeneration. The type of the transformant is not limited as long as the recombinant expression vector of the present invention can be introduced to express CgIDH and/or AvIDH. Examples of the transformant may be selected from strains included in genus  Escherichia , genus  Salmonella , genus  Shigella , genus  Enterobacter , genus  Proteus , genus  Pseudomonas , genus  Moraxella , genus  Helicobacter , genus  Stenotropomonas , genus Bdellovibrio, genus  Legionella , genus  Neisseria , and genus  Erwinia . Specific examples of the transformant may be  E. coli , and more specifically,  E. coli  BL21 (DE3). 
     When the transformant is produced, a transformation method may be performed by conventional methods in the art, for example, but is not limited to, a natural introduction method, a heat shock method, an electric shock method, etc. 
     The present invention provides a method for producing a recombinant protein including culturing the transformant, and more specifically, the method for producing the recombinant protein includes producing the recombinant expression vector for NADPH regeneration as described above; transforming the recombinant expression vector to produce a transformant; culturing the transformant to overexpress isocitrate dehydrogenase originated from  Corynebacterium glutamicum  or isocitrate dehydrogenase derived from  Azotobacter vinelandii ; and recovering the overexpressed recombinant protein. 
     Culture conditions are not particularly limited when the transformant is cultured, but may be used by introducing known culture conditions. As a specific example, the culture may be performed at 28 to 32° C., preferably 29 to 31° C., and more preferably 30° C., and the soluble expression of 90% or more of the target protein may be implemented in the culture temperature range described above. A medium for culturing microorganisms may also be appropriately introduced and used into a known medium, and as a specific example, a Luria-Bertani (LB) medium may be used, but is not limited thereto. 
     When the transformant expresses the recombinant protein by the introduction of the recombinant expression vector, the culture medium may further contain an appropriate antibiotic for selection of a transformed microorganism, and may further contain a substance for promoting expression of the recombinant protein, for example, but is not limited to, isopropyl β-D-1-thiogalactopyranoside (IPTG), etc., if necessary. 
     The method for producing the recombinant protein may be obtained by separating and purifying the recombinant protein from the culture of the transformant, wherein the culture may be the transformant or a culture medium thereof, and the culture medium may be a medium containing the transformant or a medium obtained by separating the transformant. 
     In addition, for easy separation and purification of the recombinant protein, the transformant may be destroyed, and as specific methods of destruction, methods, such as, but is not limited to, physical destruction through ultrasonic decomposition or chemical destruction through a non-ionic detergent (surfactant), etc., may be used. 
     In addition, the method for preparing the recombinant protein may further include isolating and purifying CgIDH and/or AvIDH, and the isolating and purifying may be performed by introducing conventional separation and purification processes in the art, which is performed to utilize the expressed protein for desired purpose or use. Through such separation and purification processes, a high yield of recombinant protein may be obtained. 
     The present invention provides a method for regenerating NADPH, including regenerating NADPH by adding the recombinant protein to an NADPH-dependent enzyme reaction system, an NADPH-regeneration system, and a method for regenerating NADPH, which is the cofactor of the NADPH-dependent enzyme, such as cytochrome P450. 
     Specific examples of the NADPH-dependent enzyme may be, but are not limited to, any one or two or more selected from the group consisting of dehydrogenase, reductase, oxidoreductase, transhydrogenase, peroxidase, oxygenase, monooxygenase, flavodoxin, and dehalogenase, preferably dehydrogenase. 
     The NADPH-dependent enzyme may be recombined and fused to CgIDH and/or AvIDH, or may be linked by a chemical linker. The chemical linker may be selected from, but is not limited to, the group consisting of BS(PEG)5, BS(PEG)9, BS2G-d0, BS2G-d4, DSBU, DFDNB, DMP, DMS, DSG, DSP, DSS, DSSO, DST, DTBP, EGS, TSAT, and EDC. 
     The present invention provides a kit for NADPH regeneration, including the recombinant protein. 
     In addition, the present invention provides a composition for substrate hydroxylation comprising the recombinant protein; and a NADPH dependent cytochrome P450 protein. Here, the recombinant protein may refer to, but is not limited to, a NADPH regeneration-related construct (system) including the same. Specific examples of the substrate may be selected from, but is not limited to, the group consisting of omeprazole, omeprazole sulfide, ethoxycoumarin, and nitrophenol. 
     The composition for substrate hydroxylation not only may include an NADPH-regeneration system using CgIDH and/or AvIDH to provide expensive NADPH used for cytochrome P450, but may also be used as a biological catalyst for a hydroxylation reaction of a wide range of substrates including cytochrome P450 protein by genetic fusion. 
     The present invention provides an in vitro toxicity test method including treating the composition for substrate hydroxylation. Here, the type of toxicity test is not particularly limited, but may include a drug toxicity test, a liver toxicity test, etc. 
     The present invention provides a method of converting a target substrate by co-expressing or fusion expressing the recombinant isocitrate deyhydrogenase protein and the NADPH-dependent enzyme. 
     Hereinafter, the content of the present invention will be described in more detail through examples. The examples are only for describing the present invention in more detail, and the scope of the present invention is not limited thereto. 
     Strain, Reagent, Material, and Experimental Protocol 
     In the present invention, reagents, materials, and protocols used for polymerase chain reaction (PCR), DNA cloning, transformation, etc. are as follows, which will be apparent to those skilled in the art. 
       Corynebacterium glutamicum  ATCC13032 was obtained from the American Type Culture Collection (ATCC, USA), an international depository organization, and used. 
       Azotobacter vinelandii  KACC10899 was obtained from the Korean Agricultural Culture Collection (KACC, Korea), and used. 
       E. coli  XL1-Blue was purchased from Yeastern Biotech. (Taiwan), and used. 
       E. coli  BL21 (DE3) was purchased from Yeastern Biotech. (Taiwan), and used. 
     pET24a plasmid was purchased from New England Labs (UK), and used. 
     A PureLink™ Genomic DNA Kit was purchased from Thermo Fisher Scientific Korea (Korea), and used. 
     Primers for gene amplification were synthesized by BIONICS (Korea), and used. 
     Speed-Pfu DNA Polymerase was purchased from NanoHelix Co., Ltd. (Korea), and used. 
     An In-Fusion®HD cloning kit was purchased from Takara Korea Biomedical Inc., and used. 
     Other NdeI and XhoI restriction enzymes were purchased from Takara Korea Biomedical Inc. (Korea), and used. 
     The other reagents were purchased from Sigma-Aldrich (USA), etc., and used. 
     Transformant 
       E. coli  XL1-Blue was used as the transformant for plasmid transformation and genetic manipulation. 
       E. coli  BL21 (DE3) was used as the transformant for protein expression. 
     Histidine Tag (His-Tag) 
     Since fusion of a histidine tag to an amino terminus (N-terminus) of a recombinant protein may affect the expression and the structure of a whole protein in some cases, primers were synthesized so that the histidine tag is fused to a carboxyl terminus (C-terminus). 
     Example 1 
     Construction of Recombinant Vector for Overexpression and Production of Recombinant Protein 
     Plasmid construction was performed based on standard DNA manipulation techniques. First, a PureLink™ Genomic DNA Kit was used to extract each genomic DNA from  Corynebacterium glutamicum  ATCC13032 and  Azotobacter vinelandii  KACC10899. Thereafter, PCR was performed using the extracted genomic DNA as templates. 
     Here, for the PCR reaction, primers composed of each sequence in Table 1 below were each synthesized and used. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 SEQ 
                   
                   
                   
               
               
                 ID 
                   
                   
                 Restriction 
               
               
                 No. 
                 Primer name 
                 Sequence (5′→3′) 
                 enzyme 
               
               
                   
               
             
            
               
                 3 
                 CgIDH infusion 
                 5′-GAA GGA GAT ATA CAT ATG GCT AAG ATC ATC TGG ACC 
                 NdeI 
               
               
                   
                 F 
                 CG-3′ 
                   
               
               
                   
               
               
                 4 
                 CgIDH infusion 
                 5′-GTG GTG GTG GTG CTC GAG CTT CTT CAG TGC GTC 
                 XhoI 
               
               
                   
                 R 
                 AAC GAT CTC-3′ 
                   
               
               
                   
               
               
                 5 
                 AvIDH infusion 
                 5′-GAA GGA GAT ATA CAT ATG TCC ACA CCG AAG ATT ATC 
                 NdeI 
               
               
                   
                 F 
                 TAT ACG C-3′ 
                   
               
               
                   
               
               
                 6 
                 AvIDH infusion 
                 5′-GTG GTG GTG GTG CTC GAG TGC AAG AGG TGC CAG 
                 XhoI 
               
               
                   
                 R 
                 AGC C-3′ 
               
               
                   
               
            
           
         
       
     
     Using primers of SEQ ID NOs: 3 and 4 with the template of genomic DNA extracted from  Corynebacterium glutamicum  ATCC13032, polynucleotide 1 encoding an isocitrate dehydrogenase protein from  Corynebacterium glutamicum  (CgIDH) was amplified by PCR. Using primers of SEQ ID NOs: 5 and 6 with the template for genomic DNA extracted from  Azotobacter vinelandii  KACC10899, polynucleotide 2 encoding an isocitrate dehydrogenase protein from  Azotobacter vinelandii  (AvIDH) was amplified in the same manner. During the PCR amplification, a Speed-Pfu DNA polymerase, which is a polymerase having a low mutation frequency, was used. 
     DNA fragments obtained through PCR were cloned into pET24a plasmids treated with NdeI and XhoI restriction enzymes, respectively, using an In-Fusion® HD cloning kit. The results are shown in  FIGS.  2 A and  2 B . 
     Each of  FIGS.  2 A and  2 B  illustrates schematic diagrams of the recombinant vector for transcribing and translating genes (cgIDH and avIDH) encoding amino acid sequences of SEQ ID NO: 1 and SEQ ID NO: 2, under the control of a T7 promoter. 
     Example 2 
     Establishment of Expression Conditions and Purification of Recombinant Protein 
     Establishment of Expression Conditions of Recombinant Protein 
     In order to provide high expression conditions for purification of the recombinant protein, the expression conditions were established while confirming an expression pattern of the IDH protein. 
     The recombinant expression vectors, pET24a-CgIDH and pET24a-AvIDH constructed in Example 1 above were transformed into  E. coli  XL1-Blue, respectively, using a method that is apparent to those skilled in the art, plated on an LB solid medium containing 50 ug/mL kanamycin, and then cultured overnight at 37° C. Then,  E. coli  XL1-Blues into which the recombinant expression vectors were introduced, were each inoculated into an LB liquid medium containing 50 ug/mL of kanamycin, and the recombinant expression vectors were purely isolated from the harvested bacteria by centrifuging the cultured bacteria at 220 rpm at 37° C. 
     The recombinant expression vectors isolated through the above process were each transformed into  E. coli  BL21 (DE3), plated on the LB solid medium containing 50 ug/mL of kanamycin, and then cultured overnight at 37° C. Thereafter, a single clone grown in the medium was inoculated into the LB liquid medium containing 50 ug/mL of kanamycin, and then absorbance (OD 600 ) was measured at 600 nm while being pre-cultured at 220 rpm at 37° C. 
     When the absorbance of a culture solution reached 2.0 to 2.5, after passage to the LB liquid medium having the same composition, the culturing was performed until the absorbance reached 0.6. Thereafter, 100 mM IPTG was added so that a final concentration was 0.2 mM, and the medium was incubated for further 2.5 hours at 220 rpm at 37° C. and 30° C. After completion of the culture cells were harvested by centrifugation and then adjusted to be 2.0 of OD 600  for complete washing with DDW. 
     The cells were resuspended in 200 uL of 1× phosphate-buffered saline (PBS, pH 7.4), and then disrupted by sonication. Immediately after crushing, the whole protein fractions were taken and centrifuged at 16,000×g at 4° C. for 30 minutes to remove insoluble aggregates, and aliquoted soluble fractions. 
     To the samples taken in each step, 5× sample loading buffer (0.225 M Tris-HCl pH 6.8, 50% glycerol, 5% SDS, 0.005 M bromophenol blue, and 0.25 M dithiothreitol (DTT)) was added in a ratio of 5:1, and the resulting samples was heated at 95° C. for 15 minutes to induce denaturation of the whole proteins. Then, after slowly cooling each sample, the prepared sample was loaded on a 10% acrylamide gel and fixed at 150V, followed by electrophoresis. After completion of the electrophoresis, the acrylamide gel was stained with a Coomassie Brilliant Blue solution, and expression patterns of CgIDH and AvIDH depending on culture temperature were compared and shown in  FIGS.  3 A and  3 B . 
     Each of  FIGS.  3 A and  3 B  is the SDS-PAGE analysis result for confirming the expression patterns after expressing CgIDH and AvIDH in  E. coli  BL21 (DE3) under differently set induction temperate at 30° C. and 37° C., respectively. As a result, when CgIDH was expressed at 30° C., a soluble overexpressed band was confirmed at a position of about 80 kDa, and when AvIDH was expressed at 30° C., a soluble overexpressed band was confirmed at a position of about 70 kDa. It was confirmed from these results that soluble expression did not occur when the expression temperature of both of the recombinant proteins was set to 37° C., but 90% or more soluble expression was achieved when the expression temperature was set to 30° C. 
     Purification of Recombinant Protein 
     For the purification of the protein expressed as described above, after increasing culture volume to 100 mL, the culturing was performed in the same procedure as the above culture method. 
     Each of the cells harvested by the procedure as described above was resuspended by adding 40 mL of 60 mM potassium phosphate buffer (pH 7.7) containing 300 mM sodium chloride. The resuspended cells were destroyed by sonication, and centrifuged at 16,000×g at 4° C. for 60 minutes to separate supernatant from which the insoluble aggregates were removed. Thereafter, 40 mL of soluble protein solutions were each loaded onto a 5 mL Histrap column (GE Healthcare Life Science, USA). After completion of loading of each of soluble protein fractions, they were sufficiently washed with the same buffer, and the recombinant protein was eluted by gradient to a concentration of 250 mM imidazole. 
       FIGS.  4 A and  4 B  is a result of SDS-PAGE that can confirm a purification result of CgIDH and AvIDH using affinity chromatography. It was confirmed from  FIGS.  4 A and  4 B  that CgIDH was eluted at a concentration of about 40 to 60 mM imidazole, and AvIDH was eluted at a concentration of about 90 to 110 mM imidazole. In particular, it was confirmed that both of the eluted CgIDH and AvIDH were purified with a high purity of 95% or more. 
     Additionally, as a result of quantifying the protein of an eluted fraction by a protein quantification test (Bradford assay), it was confirmed that both recombinant proteins exhibited a purification yield of 1 g/L, indicating a high yield even in laboratory-level purification in which culture conditions were not optimized. 
     Example 3 
     Quaternary Structure of Purified Recombinant Protein 
     In order to confirm whether a multimer (quaternary structure) of the recombinant protein purified by the process as described above is formed, size exclusion chromatography was performed. 
     First, after CgIDH and AvIDH purified in Example 2 were each loaded onto a Superdex™ 200 10/300 GL column (GE Healthcare Life Science, USA), size exclusion chromatography was performed using 1×PBS (pH 7.4). Cytochrome P450 BM3 (blue, 119 kDa) was used as a control group, and conalbumin (purple, 75 kDa) and ovalbumin (orange, 45 kDa) were used as standard size markers. The results of performing size exclusion chromatography are shown in  FIG.  5   . 
     It was confirmed from  FIG.  5    that CgIDH and AvIDH were eluted at the peak position consistent with the SDS-PAGE analysis result, which means that both recombinant proteins have a monomeric form. 
     Example 4 
     Kinetic Constant Analysis of Purified Recombinant Protein 
     The analysis of kinetic properties related to an enzyme activity of the recombinant protein, that is, a kinetic constant, was performed by the following procedure. 
     The analysis of kinetic activity for each of the recombinant proteins purified in Example 2 was performed based on the method described in Chen, R. &amp; Yang, H. Biochemistry and Biophysics, 383(2):238-245 (2000); and Watanabe, S. Microbiology 151(4):1083-1094 (2005). 
     Here, a K m  (uM) value representing the affinity of the enzyme to the substrate as a reaction constant used in enzyme kinetics, a K cat (S-1) value, which means the metabolic turnover number of the enzyme, and a K cat /K m  (S-1, M-1) value representing a reaction efficiency of the enzyme, were determined. The parameters of the wild-types CgIDH and AvIDH were used as control groups, and the results are shown in  FIGS.  6 A and  6 B . 
     It was confirmed from  FIGS.  6 A and  6 B  that both CgIDH and AvIDH according to the present invention showed a slight decrease in K cat  compared with the wild-types, but the enzyme activity for providing NADPH required for the reaction of the NADPH-dependent enzyme such as cytochrome P450 was sufficiently high. 
     Thus, the activity of the recombinant protein according to the present invention can be seen to be the same level as that of the wild-types, which supports the reliability of the result of the quaternary structure analysis of Example 3. That is, the above result can be interpreted as an indirect or considerable result indicating that there was no change in the quaternary structure during the producing process of the recombinant protein. 
     Example 5 
     Specific Activity Analysis of Recombinant Protein 
     In order to confirm the degree of NADPH regeneration by the activity of the IDH recombinant protein, CgIDH and AvIDH were each added to a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate (MnSO 4 ), 0.8 mM DL-isocitric acid, and 0.5 mM NADP+ so that the final concentrations were 5 nM, and the degree of increase of NADPH depending on the enzyme activity was measured with a spectrophotometer. When fluorescence was measured using a spectrophotometer, an excitation wavelength was set to 350 nm and an emission wavelength was set to 450 nm, and the measurement results are shown in  FIG.  7   . 
     It was confirmed from  FIG.  7    that NADPH increased over time in each reaction solution containing each protein of CgIDH indicated by a circle and AvIDH indicated by a square, which suggests that both CgIDH and AvIDH generate NADPH by an enzymatic reaction that converts isocitric acid to α-ketoglutarate. 
     In addition, when the enzyme activity of the same amount of the recombinant protein is compared, a CgIDH enzyme reaction slope was found to be higher than that of an AvIDH enzyme reaction slope, which means that CgIDH has higher enzyme activity. These results are also consistent with those in  FIGS.  6 A and  6 B  of Example 4. 
     From the above results, it was confirmed that the specific activities of CgIDH and AvIDH correspond to 57 U/mg and 28 U/mg, respectively. 
     Example 6 
     Analysis of Coupling Reaction Between NADPH-Regeneration System Based on Isocitrate Dehydrogenase and Cytochrome P450 BM3 
     In order to confirm whether NADPH, which is the cofactor of the NADPH-dependent enzyme, can be continuously supplied, through the NADPH-regeneration system using the IDH recombinant protein, CgIDH and cytochrome P450 BM3 were added to a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate, 40 mM DL-isocitric acid, 0.5 mM NADP, and 2 mM omeprazole to prepare a reaction product, and the reaction product was prepared using AvIDH and cytochrome P450 BM3 in the same manner. Thereafter, coupling reactions between CgIDH and AvIDH, and cytochrome P450 BM3 were performed at 37° C. for each reaction to prepare the product. 
     NADPH Self-Fluorescence Analysis to Confirm Cofactor Regeneration 
     In the above process, 2 nM CgIDH and 500 nM cytochrome P450 BM3 were each added to the reaction solution at the final concentrations, and 2 nM AvIDH and 500 nM cytochrome P450 BM3 were each added to the reaction solution at the final concentration in the same manner. Thereafter, after each reactant was reacted at 37° C., whether or not NADPH was increased was measured using the spectrophotometer. When fluorescence was measured using the spectrophotometer, an excitation wavelength was set to 350 nm and an emission wavelength was set to 450 nm, and the measurement results are shown in  FIGS.  8 A and  8 B . 
     Here, the case in which the IDH recombinant protein was not added to the reaction solution was used as a negative control group (circle in  FIG.  8 A ), and two cases in which cytochrome P450 BM3 was not added to the reaction solution were used as positive control groups (square and triangle in  FIG.  8 A ). 
       FIG.  8 B  illustrates fluorescence measurement results for two coupling reactions (CgIDH and cytochrome P450 BM3 (square); AvIDH and cytochrome P450 BM3 (triangle)) together with the negative control group (circle), wherein a fluorescence intensity scale on a vertical axis (y-axis) is set from 0 to 500 a.u. and is enlarged. 
     It was confirmed from  FIGS.  8 A and  8 B  that only in the case of the reaction solution in which both of the coupled proteins were present, the fluorescence intensity slightly increased due to NADPH generated by the IDH recombinant protein at the beginning of the reaction, but the fluorescence intensity remained at a certain level after a certain period of time, which suggests that NADPH produced by the IDH recombinant protein is consumed by cytochrome P450 BM3, which is the NADPH-dependent enzyme and NADP produced at the same time is again regenerated into NADPH by the IDH recombinant protein, thereby efficiently regenerating the cofactor, NADPH. A schematic representation of a reaction involving IDH recombinant protein, NADPH-dependent enzyme, NADP+, and NADPH in terms of regeneration of NADPH, is shown in Scheme 1 below: 
       NADP + +IDH recombinant protein→NADPH+NADPH-dependent enzyme→NADP +   Scheme 1
 
     Determination of Enzyme Concentration Ratio 
     In the above reaction, the amount of cytochrome P450 BM3 was high compared with the IDH recombinant protein, so NADPH was present in a small concentration in the reaction solution. Thus, in order to establish a more appropriate enzyme concentration ratio, 500 nM cytochrome P450 BM3 was added to a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate, 40 mM DL-isocitric acid, 0.5 mM NADP, and 2 mM omeprazole, and CgIDH and AvIDH were each added at 2 nM, 5 nM, and 10 nM (concentration ratio of 1:250, 1:100, 1:50, respectively) to prepare a reaction product. Thereafter, each reactant was subjected to a coupling reaction at 37° C., and then the degree of increase of NADPH was measured in the same manner. The results are shown in  FIGS.  9 A and  9 B . 
       FIG.  9 A  illustrates the result of the coupling reaction between CgIDH and cytochrome P450 BM3, wherein the concentration ratio of the two enzymes was set to 1:250 (square), 1:100 (triangle) and 1:50 (inverted triangle). In addition,  FIG.  9 B  illustrates the result of the coupling reaction between AvIDH and cytochrome P450 BM3, wherein the concentration ratio of the two enzymes was set to 1:250 (square), 1:100 (triangle) and 1:50 (inverted triangle). In the same manner as in  FIGS.  8 A and  8 B , the case in which the IDH recombinant protein was not added to the reaction solution was used as the negative control group (circle in  FIGS.  9 A and  9 B ). 
     As can be seen from  FIGS.  9 A and  9 B , an interval in which NADPH was maintained at a certain level was different depending on the concentration of CgIDH and AvIDH, and subsequent analysis was performed by setting the ratio of an enzyme concentration (for CgIDH, 1:50 and for AvIDH, 1:100) at which the fluorescence intensity was maintained at 2000 a.u. as the ratio of an appropriate enzyme concentration. 
     HPLC Analysis of Hydroxylation Product of Substrate 
     In the above reaction, in order to confirm that the activity of cytochrome P450 BM3 is maintained by substantial NADPH regeneration, and the hydroxylation reaction of omeprazole, which is one of the substrates, occurs, to 1 mL of a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate, 40 mM DL-isocitric acid, 0.5 mM NADP, and 2 mM omeprazole, CgIDH and cytochrome P450 BM3 were added so that the final concentrations were 10 nM and 500 nM, respectively, and AvIDH and cytochrome P450 BM3 were added so that the final concentrations were 5 nM and 500 nM, respectively, to prepare a reaction product. 
     The reaction mixture was recovered by 90 uL each time, mixed with 90 uL of methanol to stop the reaction, and then HPLC analysis was performed. Specific HPLC performance conditions are as follows:
         HPLC was performed using an Alliance HPLC system (Waters).   A SunFire 18C column was used as a column   The amount of sample loading was set to 20 uL.   As a HPLC mobile phase, 30% acetonitrile was flowed at a flow rate of 1 mL/min, and an eluate was measured with ultraviolet (UV) light at 302 nm.   Analysis was performed using an Empower 3 (Waters) program.       

     Instead of using the NADPH-regeneration system as a control group, NADPH itself and a substrate were added to perform the hydroxylation reaction of the substrate through cytochrome P450 BM3 activity, and HPLC analysis was performed in the same manner. The results are shown in  FIGS.  10 A- 10 F . 
     It was confirmed from  FIGS.  10 A- 10 F  that the product of the coupling reaction, that is, 5′-hydroxyomeprazole, which is a hydroxylated form of the substrate omeprazole, was eluted from all three reaction solutions (a coupling reaction between CgIDH and cytochrome P450 BM3, a coupling reaction between AvIDH and cytochrome P450 BM3, control) when five minutes has elapsed, and the shape of each peak was similar. 
     In addition, the elution amount of 5′-hydroxyomeprazole produced by the coupling reaction (5 min) with the NADPH-regeneration system of the present invention was measured to be 126% in the case of the coupling reaction between CgIDH and P450 BM3, and 114% in the case of the coupling reaction between AvIDH and P450 BM3, based on the elution amount of 5′-hydroxyomeprazole produced in the control group. 
     The above-mentioned elution amount suggests that the NADPH-regeneration system of the present invention may more effectively supply NADPH to the enzymatic reaction of the NADPH-dependent enzyme. 
     Example 7 
     Storage Stability of Recombinant Protein 
     In order to evaluate the stability of the recombinant protein produced in the present invention, after a certain period of time, each of the recombinant proteins stored at 4° C. was added to a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate, 40 mM DL-isocitric acid, and 0.5 mM NADP+ so that the final concentration was 5 nM, the reaction was proceeded as described in Example 5, and the degree of increase of NADPH was measured. The measurement results are shown in  FIG.  11   . 
     It was confirmed from  FIG.  11    that after storage at 4° C. for 30 days, the enzyme activity of the CgIDH and AvIDH recombinant proteins measured under the same conditions did not decrease. 
     In particular, it was confirmed that the activity increased by 10 to 20% compared with before storage, which suggests that the activity is maintained in the range of 90 to 110% of the initial activity, considering that a deviation occurs depending on reaction conditions and protein quantification. 
     That is, it was confirmed that the NADPH-regeneration system of the present invention may be stably utilized as an independent component for an NADPH-dependent enzymatic reaction, and may be applied as key parts by maintaining favorable stability for mass production and long-term storage in an NADPH-regeneration process for NADPH-dependent enzyme activity including cytochrome P450 BM3. 
     Example 8 
     Enzyme Activity Inhibitory Effect Depending on Product of Recombinant IDH Protein 
     In order to confirm an enzyme activity inhibitory effect by α-ketoglutarate, which is an enzyme reaction product of the recombinant protein produced in the present invention, a reaction product, in which 5 nM of CgIDH and 5 nM AvIDH were each added to a reaction solution containing 100 mM potassium phosphate buffer (pH 7.4), 0.8 mM manganese sulfate, 40 mM DL-isocitric acid, and 0.5 mM NADP, was prepared. Thereafter, α-ketoglutarate was added for each concentration to proceed the reaction as described in Example 5, and the degree of increase of NADPH was measured. The measurement results are shown in  FIG.  12   . Here, an experimental group to which α-ketoglutarate was not added was used as a control group. 
     It was confirmed from  FIG.  12    that for CgIDH, the enzyme activity was reduced by 30% by the added 10 mM α-ketoglutarate, and for AvIDH, the enzyme activity was reduced by 30% by the added 20 mM α-ketoglutarate. 
     The above-mentioned reduction means that when the NADPH-regeneration system is operated in a batch process, an enzyme activity inhibition phenomenon may occur due to the enzyme reaction product, which suggests that it is preferable to perform a process of removing the enzyme reaction product by introducing a continuous process, a hollow tube membrane reactor, etc. in order to solve the above phenomenon. However, it was also confirmed that when the pH of the reaction process is corrected by adding a pH adjuster, etc., the inhibitory effect can be improved by 50% or more (results not attached). 
     Example 9 
     Analysis of Coupling Reaction Between NADPH-Regeneration System and Cytochrome P450 BM3 Depending on Substrate Change 
     In Example 6, the substrate omeprazole was changed to omeprazole sulfide, ethoxycoumarin, and nitrophenol, respectively, and then NADPH-regeneration ability was analyzed under the same conditions. 
     As a result, the same substrate conversion result was confirmed even when the substrates other than omeprazole were used, which suggests that the NADPH-regeneration system using the IDH recombinant protein, regardless of the type of substrate, has the NADPH-regeneration ability to maintain NADPH-dependent enzyme activity. That is, it can be said that it is suitable as robust key parts of the NADPH-regeneration system. 
     Example 10 
     Analysis of Coupling Reaction Depending on Changes in NADPH-Regeneration System and NADPH-Dependent Enzyme 
     In Example 6, after changing cytochrome P450, which is the NADPH-dependent enzyme, to mannitol 2-dehydrogenase, methylmalonate-semialdehyde dehydrogenase, glutamate dehydrogenase, and phenylalanine dehydrogenase, respectively, the NADPH-regeneration ability was analyzed under the same conditions. 
     As a result, the same results were confirmed for other types of NADPH-dependent enzymes other than cytochrome P450 BM3, which suggests that the NADPH-regeneration system using the IDH recombinant protein, regardless of the type of NADPH-dependent enzyme, has the NADPH regeneration ability to maintain NADPH-dependent enzyme activity. That is, it can be said that it is suitable as robust key parts of the NADPH-regeneration system. 
     Example 11 
     Whole Cell Reaction Analysis Through Co-Expression of Recombinant IDH Protein and Cytochrome P450 
     Transformants transformed with a plasmid in which the IDH recombinant protein according to the present invention and cytochrome P450 BM3 are co-expressed, were cultured as in the above Example, and 0.8 mM manganese sulfate, 2 mM omeprazole, a sufficient amount of potassium phosphate buffer (pH 7.4), DL-isocitric acid, and 0.5 mM NADP were added to a reaction solution with harvested cells after cultivation. Thereafter, HPLC analysis was performed in the same manner as in the above Example. 
     As a result, it was confirmed that 5′-hydroxyomeprazole was detected in reaction solution, which suggests that substrate conversion is possible even through a whole-cell reaction in which the NADPH-regeneration system using the IDH recombinant protein and the NADPH-dependent enzymes are simultaneously expressed. 
     Example 12 
     Whole Cell Reaction Analysis Through Fused Protein Expression of Recombinant IDH Protein with Cytochrome P450 
     Transformants transformed with a plasmid engineered so that the IDH recombinant protein according to the present invention and cytochrome P450 BM3 are expressed as a fusion protein in cells, were cultured as in the above Example. 0.8 mM manganese sulfate, 2 mM omeprazole, a sufficient amount of potassium phosphate buffer (pH 7.4), DL-isocitric acid, and 0.5 mM NADP were added to a reaction solution with harvested cells after cultivation. Thereafter, HPLC analysis was performed in the same manner as in the above Example. 
     As a result, it was confirmed that 5′-hydroxyomeprazole was produced by whole cell catalyst, which suggests that substrate conversion is possible even through the whole-cell reaction in which the NADPH-regeneration system using the IDH recombinant protein and the NADPH-dependent enzymes are expressed as a fusion protein. 
     The above results show that the difficulty of efficient regeneration of NADPH through the expression of fusion protein, which is one of the fundamental disadvantages of the conventional cytochrome P450 BM3 and the NADPH-regeneration system (e.g., G6PDH, etc), has been overcome, through the fusion protein expression of the NADPH-regeneration system using the IDH recombinant protein and the NADPH-dependent enzyme. In the future, the continuous reaction system with NADPH-regeneration part f, which fused the NADPH-dependent enzyme with IDH recombinant protein as a single protein, can be widely used in the development of new processes with excellent productivity. 
     The present invention relates to a recombinant vector including a polynucleotide encoding an isocitrate dehydrogenase recombinant protein from  Corynebacterium glutamicum  and an isocitrate dehydrogenase recombinant protein from  Azotobacter vinelandii , a method for producing the recombinant protein, and an NADPH-regeneration system using the recombinant protein produced by the method. In the present invention, the enzyme in a monomeric form that may be efficiently used in the NADPH-regeneration system in the transformant into which the recombinant vector was introduced, was found, and the NADPH-regeneration system using the enzyme in a monomeric form has a very high utility value as biological parts and biocatalyst materials that provides NADPH to the NADPH-dependent enzyme. 
     Special portions of contents of the present invention have been described in detail herein above, and it will be obvious to those skilled in the art that this detailed description is only an exemplary embodiment and the scope of the present invention is not limited by this detailed description.