Method For Producing Carotenoids Each Having 50 Carbon Atoms
20170191103 ยท 2017-07-06
Assignee
Inventors
- Daisuke Umeno (Chiba, JP)
- Maiko Furubayashi (Chiba, JP)
- Norihiko MISAWA (Ishikawa, JP)
- Shinichi Takaichi (Kanagawa, JP)
Cpc classification
C12P23/00
CHEMISTRY; METALLURGY
C12P5/026
CHEMISTRY; METALLURGY
Y02P20/52
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
C12Y205/0101
CHEMISTRY; METALLURGY
International classification
C12P23/00
CHEMISTRY; METALLURGY
Abstract
The present invention provides a method of producing a carotenoid having 50 carbon atoms which comprises culturing, in a medium, a cell transformed with a mutant phytoene desaturase gene and obtaining the carotenoid having 50 carbon atoms from the culture. The mutant phytoene desaturase gene has an introduced mutation to encode a mutant phytoene desaturase having an enhanced activity to desaturate a carotenoid backbone compound of 50 carbon atoms.
Claims
1-15. (canceled)
16. A method of producing a carotenoid having 55 carbon atoms, comprising: culturing, in a medium, a cell transformed with a mutant diapophytoene synthase gene and a mutant farnesyl diphosphate synthase gene; and obtaining the carotenoid having 55 carbon atoms from a culture after the culturing, wherein the transformation is performed by a plasmid having a nucleotide sequence of SEQ ID NO: 26 that contains the mutant diapophytoene synthase gene and a plasmid having a nucleotide sequence of SEQ ID NO: 25 that contains the mutant farnesyl diphosphate synthase gene.
17. A method of producing a carotenoid having 60 carbon atoms, comprising: culturing, in a medium, a cell transformed with a mutant diapophytoene synthase gene and a mutant hexaprenyl diphosphate synthase gene; and obtaining the carotenoid having 60 carbon atoms from a culture after the culturing, wherein the transformation is performed by a plasmid having a nucleotide sequence of SEQ ID NO: 26 that contains the mutant diapophytoene synthase gene and a plasmid having a nucleotide sequence of SEQ ID NO: 24 that contains the mutant farnesyl diphosphate synthase gene.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION OF THE INVENTION
[0061] First, carotenoid biosynthetic pathways are described (see
[0062] In a pathway for synthesizing a carotenoid having 40 carbon atoms, phytoene is synthesized by condensation of two molecules of C.sub.20PP with a phytoene synthase (CrtB), and serves as a precursor for a carotenoid (carotenoid backbone compound).
[0063] Phytofluene, -carotene, neurosporene, lycopene, tetradehydrolycopene, and the like are synthesized by sequential desaturation of phytoene. Various carotenoids such as -carotene, -carotene, -carotene, -carotene, -carotene, lutein, zeaxanthin, canthaxanthin, fucoxanthin, astaxanthin, antheraxanthin, and violaxanthin are synthesized by modification of the ends of lycopene through cyclization or oxidation. It should be noted that carotenoids constructed only of carbon and hydrogen are classified as carotenes, while carotenoids containing an oxygen element in addition to carbon and hydrogen are classified as xanthophylls.
[0064] The present invention enables production of a carotenoid having 50 carbon atoms by alteration of biosynthetic pathways for carotenoids present in nature, and is directed to a production method for a carotenoid having 50 carbon atoms, wherein the production method comprises: culturing, in a medium, a cell transformed with a mutant phytoene desaturase gene; and obtaining a carotenoid having 50 carbon atoms from a culture after the culturing. It should be noted that, in this description, 50 carbon atoms is sometimes simply referred to as C.sub.50, and the same applies to, for example, 35, 40, 45, 55, and 60 carbon atoms.
[0065] In this description, the carotenoid having 50 carbon atoms is distinguished from a carotenoid backbone compound of 50 carbon atoms to be desaturated by a mutant phytoene desaturase, and refers to a compound whose number of double bonds has been increased by one or more by the desaturation of the carotenoid backbone compound of 50 carbon atoms. The carotenoid having 50 carbon atoms may undergo any modification, and also includes, for example, one having a ring or an s ring at its ends, and one having a functional group containing an element other than carbon and hydrogen, such as a hydroxyl group or a keto group. Further, the carotenoid having 50 carbon atoms may be any carotenoid as long as the number of carbon atoms derived from a backbone compound is 50, and also includes, for example, one in which the total number of carbon atoms is 50 or more as a result of the addition of a functional group containing carbon, such as a methyl group or an acetyl group, by modification.
[0066] The carotenoid backbone compound of 50 carbon atoms is a precursor for the carotenoid having 50 carbon atoms, which may be desaturated by a mutant phytoene desaturase. Specific examples of the carotenoid backbone compound of 50 carbon atoms include: C.sub.50-carotene (n=3) (16,16-diisopentenylphytoene); and compounds in which the number of conjugated double bonds in C.sub.50-carotene (n=3) is increased by 1 to 5. Specific examples of the compounds in which the number of the double bonds in C.sub.50-carotene (n=3) is increased by 1 to 5 include: C.sub.50-carotene (n=5), which is obtained by increasing the number of the double bonds by 1; C.sub.50-carotene (n=7), which is obtained by increasing the number of the double bonds by 2; and C.sub.50--carotene (n=11) and C.sub.50-neurosporene (n=13) in
[0067] In this description, the carotenoid backbone compound of 50 carbon atoms that has been desaturated by a mutant phytoene desaturase but has not undergone any modification afterwards is referred to as desaturated carotenoid having 50 carbon atoms. The desaturated carotenoid having 50 carbon atoms is a linear compound that does not have any functional group except for that derived from a backbone compound. The desaturated carotenoid having 50 carbon atoms is encompassed by the carotenoid having 50 carbon atoms. Specific examples of the desaturated carotenoid having 50 carbon atoms include compounds in which the number of double bonds in C.sub.50-carotene (n=3) is increased by 1 to 6, and do not include C.sub.50-carotene (n=3) itself. It should be noted that the compound in which the number of the double bonds in C.sub.50-carotene (n=3) is increased by 6 is C.sub.50-lycopene (n=15).
[0068] Further, in this description, the term compound having a carotenoid backbone of 50 carbon atoms is used in some cases as a concept including all of the carotenoid having 50 carbon atoms, the carotenoid backbone compound of 50 carbon atoms, the desaturated carotenoid having 50 carbon atoms, and the like.
[0069] The mutant phytoene desaturase that catalyzes a reaction for desaturating the carotenoid backbone compound of 50 carbon atoms is obtained by inducing a mutation in a wild-type phytoene desaturase (CrtI). The phytoene desaturase (CrtI) is an enzyme that desaturates phytoene having 40 carbon atoms. In nature, CrtI catalyzes a synthesis reaction of lycopene that contains 11 conjugated double bonds, by desaturating phytoene that contains 3 conjugated double bonds to sequentially introduce double bonds. The mutant phytoene desaturase in the present invention has an enhanced activity to desaturate the C.sub.50 carotenoid backbone compound as compared to the wild-type phytoene desaturase by virtue of the introduction of a mutation.
[0070] The mutant phytoene desaturase in the present invention may be derived from any organisms including plants, bacteria, and the like as long as the mutant phytoene desaturase has an enhanced activity to desaturate the C.sub.50 carotenoid backbone compound by virtue of a mutation. The mutant phytoene desaturase is preferably derived from microorganisms, more preferably derived from bacteria belonging to the genus Pantoea (formerly named the genus Erwinia), still more preferably derived from Pantoea ananatis (formerly named Erwinia uredovora). The amino acid sequence of the wild-type phytoene desaturase (CrtI) derived from Pantoea ananatis is set forth in SEQ ID NO: 1 of the sequence listing.
[0071] In the present invention, a mutant phytoene desaturase gene (crtI*) encodes the mutant phytoene desaturase. A mutation in the mutant phytoene desaturase gene may be any mutation as long as it achieves the object of the present invention. The mutation preferably causes a substitution of an amino acid corresponding to at least one amino acid selected from asparagine at position 304, phenylalanine at position 339, isoleucine at position 338, aspartic acid at position 395, and isoleucine at position 228 in the amino acid sequence set forth in SEQ ID NO: 1, more preferably causes at least a substitution of an amino acid corresponding to asparagine at position 304 in SEQ ID NO: 1 by proline or serine, still more preferably causes at least a substitution of an amino acid corresponding to asparagine at position 304 in SEQ ID NO: 1 by proline. Herein, the amino acid corresponding to an amino acid at position X in SEQ ID NO: 1 defines that an amino acid as a target of the mutation is at position X counting from the N-terminus in SEQ ID NO: 1, but encompasses that the position X is expressed with a different numerical value in a phytoene desaturase having an amino acid sequence different from the amino acid sequence set forth in SEQ ID NO: 1.
[0072] The mutant phytoene desaturase gene is specifically exemplified by a phytoene desaturase gene derived from Pantoea ananatis (nucleotide sequence set forth in SEQ ID NO: 2 of the sequence listing), the nucleotide sequence having introduced therein a mutation causing a desired amino acid substitution. The mutant phytoene desaturase gene is exemplified by a gene having a nucleotide sequence of SEQ ID NO: 3 in which adenine (A) at position 911 is substituted by guanine (G) in the nucleotide sequence of SEQ ID NO: 2. The substitution of the nucleotide at position 911 causes a substitution of asparagine at position 304 in the amino acid sequence of SEQ ID NO: 1 by serine. It should be noted that SEQ ID NO: 2 has introduced therein non-synonymous mutations G1131A and A1476T. Further, the mutant phytoene desaturase gene is exemplified by a gene having a nucleotide sequence in which the nucleotide sequence AAC at positions 910 to 912 in the nucleotide sequence of SEQ ID NO: 2 is substituted by CCT, CCC, CCA, or CCG, more preferably CCT (nucleotide sequence set forth in SEQ ID NO: 28 of the sequence listing). The substitution of such bases causes a substitution of asparagine at position 304 in the amino acid sequence of SEQ ID NO: 1 by proline (amino acid sequence set forth in SEQ ID NO: 27 of the sequence listing). It should be noted that SEQ ID NO: 28 has introduced therein non-synonymous mutations G1131A and A1476T.
[0073] The nucleotide sequence of the mutant phytoene desaturase gene may be determined by producing a mutant gene library and screening a gene encoding an enzyme that has a function of interest from the library. The screening may be performed by, for example, a method described in Examples. Once the nucleotide sequence is determined, the mutant phytoene desaturase gene may be obtained by, for example, chemical synthesis, PCR using a cloned probe as a template, or a site-directed mutagenesis method.
[0074] The present invention includes the step of culturing, in a medium, a cell to be transformed with a mutant phytoene desaturase gene. The cell may be one originally harboring any other carotenoid biosynthetic gene, or may be one transformed with any other carotenoid biosynthetic gene. The other carotenoid biosynthetic gene is involved in a reaction upstream or downstream of a desaturating reaction for the C.sub.50 carotenoid backbone compound. The upstream reaction corresponds to a pathway for supplying the C.sub.50 carotenoid backbone compound, and the downstream reaction corresponds to a pathway for further modifying the C.sub.50 desaturated carotenoid.
[0075] The pathway for supplying the C.sub.50 carotenoid backbone compound is described. IPP, DMAPP, C.sub.10PP, C.sub.15PP, and C.sub.20PP can be originally synthesized in many cells, in particular, all microorganisms. It is preferred that the cell in the present invention can synthesize geranylfarnesyl diphosphate (hereinafter sometimes referred to as C.sub.25PP) from C.sub.15PP and/or C.sub.20PP, and can synthesize the C.sub.50 carotenoid backbone compound via the condensation of two molecules of C.sub.25PP. It is more preferred that the cell in the present invention be transformed with at least one of a gene encoding an enzyme that synthesizes C.sub.25PP from C.sub.15PP and/or C.sub.20PP or a gene encoding an enzyme that synthesizes the C.sub.50 carotenoid backbone compound via the condensation of two molecules of C.sub.25PP.
[0076] The gene encoding the enzyme that synthesizes C.sub.25PP from C.sub.15PP and/or C.sub.2022 may be any gene having a function of interest. Such gene is exemplified by a mutant gene of a farnesyl diphosphate synthase (FDS) derived from Geobacillus stearothermophillus, a moderate thermophilic bacterium belonging to the genus Geobacillus (Ohnuma, S. et al., J Biol Chem 271, 30748-30754 (1996), JP 2010-258989). The mutant gene is exemplified by a gene encoding a double mutant of FDS (FDS.sub.Y81A,V157A) in which tyrosine at position 81 is substituted by alanine (Y81A) and valine at position 157 is substituted by alanine (V157A) (fds.sub.Y81A,V157A: SEQ ID NO: 4 of the sequence listing).
[0077] The gene encoding the enzyme that synthesizes the C.sub.50 carotenoid backbone compound via the condensation of two molecules of C.sub.25PP may be any gene having a function of interest. Such gene is exemplified by a mutant gene of a diapophytoene synthase (CrtM) derived from Staphylococcus aureus, which synthesizes a C.sub.30 carotenoid backbone compound via the condensation of two molecules of C.sub.15PP. The mutant gene is exemplified by a gene encoding a triple mutant of CrtM (CrtM.sub.F26A,W38A,F233S) in which phenylalanine at position 26 and tryptophan at position 38 are substituted by alanine (F26A and W38A) and phenylalanine at position 233 is substituted by serine (F233S) CrtM.sub.F26A,W38A,F233S: SEQ ID NO: 5 of the sequence listing). It has been found that CrtM.sub.F26A,W38A,F233S synthesizes the C.sub.50 carotenoid backbone compound in an extremely efficient manner.
[0078] The cell of the present invention is preferably transformed with both of the gene encoding the enzyme that synthesizes C.sub.25PP from C.sub.15PP and/or C.sub.20PP and the gene encoding the enzyme that synthesizes the C.sub.50 carotenoid backbone compound from two molecules of C.sub.25PP because the cell can produce the C.sub.50 carotenoid backbone compound with high efficiency. In addition, the cell of the present invention may be transformed with a gene (idi) encoding an enzyme that isomerizes IPP into DMAPP (e.g., an isopentenyl diphosphate isomerase (Idi)) in addition to the above-mentioned genes. When the cell is transformed with the gene encoding the enzyme that isomerizes IPP into DMAPP, the production amount of the C.sub.50 carotenoid backbone compound and the specificity can be further improved.
[0079] The pathway for further modifying the C.sub.50 desaturated carotenoid is described. The C.sub.50 desaturated carotenoid is considered to correspond to lycopene or tetradehydrolycopene in nature, and it is predicted that the C.sub.50 desaturated carotenoid may be modified by various enzymes involved in the modification of lycopene. The cell in the present invention may contain a gene encoding an enzyme that cyclizes the ends of the C.sub.50 desaturated carotenoid and/or a gene encoding an enzyme that oxidizes the C.sub.50 desaturated carotenoid by oxygenation. In addition, when the cell in the present invention has the gene encoding the enzyme that cyclizes the ends of the C.sub.50 desaturated carotenoid (in particular, -cyclization), the cell may be transformed with a gene encoding an enzyme that hydroxylates a cyclic moiety (in particular, a -ring) and/or a gene encoding an enzyme that ketolates a cyclic moiety (in particular, a -ring). It should be noted that the -ring has the same meaning as a -ionone ring.
[0080] The gene encoding the enzyme that cyclizes the ends of the C.sub.50 desaturated carotenoid may be any gene having a function of interest. Such gene is exemplified by a gene (crtY) encoding a lycopene cyclase (CrtY) derived from Pantoea ananatis, which synthesizes -carotene from lycopene (Misawa N. et al., J Bacteriol 172, 6704-6712 (1990)).
[0081] In a carotenoid having -cyclized ends, a gene encoding an enzyme that hydroxylates the -ring and/or a gene encoding an enzyme that ketolates the -ring may be any gene having a function of interest. Such gene is exemplified by a -ionone ring-3-hydroxylase (CrtZ) gene (crtZ) or -ionone ring-4-ketolase (-ionone ring-4-oxygenase) (CrtW) gene (crtW) derived from a marine bacterium Paracoccus sp. strain N81106 (formerly named Agrobacterium aurantiacum) or derived from a marine bacterium Brevundimonas sp. strain SD-212 (Misawa N. et al., J Bacterial 177, 6575-6584 (1995); Nishida, Y. et al., Appl Environ Microbiol 71, 4286-4296 (2005)). A nucleotide sequence in which crtZ and crtW derived from Paracoccus sp. strain N81106 and crtY described above are combined is set forth in SEQ ID NO: 6. A -ionone ring-3-hydroxylase catalyzes a reaction for hydroxylating carbon at the 3-position of a -ring, and a -ionone ring-4-ketolase catalyzes a reaction for oxygenating carbon at the 4-position of a -ring to form a carbonyl group (keto group).
[0082] The gene encoding the enzyme that oxidizes the C.sub.50 desaturated carotenoid may be any gene having a function of interest. Such gene is exemplified by a spheroidene monooxygenase (CrtA) gene (crtA) derived from Rhodobacter sphearoides (SEQ ID NO: 7). A spheroidene monooxygenase is an enzyme that catalyzes an oxidation reaction for converting spheroidene into spheroidenone by inserting an oxygen atom.
[0083] The cell of the present invention may be transformed with genes encoding various enzymes involved in the pathway for modifying the C.sub.50 desaturated carotenoid other than those described above, depending on the kind of a carotenoid to be produced. For example, when the cell is transformed with a -ionone ring-2-hydroxylase (CrtG) gene (expressed as CrtV in WO 2005/049643 A1) derived from Brevundimonas sp. strain SD-212 (Nishida, Y. et al, Appl Environ Microbiol 71, 4286-4296, 2005), a C.sub.50 carotenoid having a -ring hydroxylated at the 2-position and the 2-position, the organic synthesis of which has been considered to be difficult, can also be produced. Further, when the cell is transformed with a zeaxanthin glucosyl transferase (crtX) gene derived from Pantoea ananatis (Misawa N, J Bacteriol 172, 6704-6712, 1990), a C.sub.50 carotenoid in which hydroxyl groups at the 3-position and 3-position of a -ring are glycosidized can also be produced.
[0084] A cell capable of producing a C.sub.50 carotenoid in the present invention may be produced by selecting an appropriate expression vector and employing a known foreign gene introduction and expression method (e.g., Sambrook, J., Russel, D. W., Molecular Cloning A Laboratory Manual, 3rd Edition, CSHL Press, 2001). The cell is obtained by: preparing a gene to be introduced into the cell by transformation by using a conventional method such as a PCR method; incorporating the gene into an expression vector suitable for a host by using a conventional method; selecting a vector of interest; and transforming a host cell with the vector by using a conventional method. When transforming a cell with two or more kinds of genes, the cell may be transformed with the plurality of genes incorporated into the same expression vector, or may be cotransformed with the plurality of genes incorporated into different expression vectors.
[0085] The cell serving as the host is not limited, but microorganisms such as E. coli, Bacillus subtilis, and yeast are preferred in view of shortening of a culturing time and ease of cloning. In particular, E. coli and yeast are preferred. Suitable examples of the E. coli include: cloning strains such as Escherichia coli XL1-Blue (hereinafter simply referred to as E. coli XL1-Blue); expression strains such as HB101 and BL21; and gene knockout strains in which the synthesis amount of a terpene precursor is large, such as JW1750 gdhA (glutamate dehydrogenase-deficient) and JW0110 aceE (pyruvate dehydrogenase-deficient) (Baba, T. et al.; Mol Syst Biol 2, 2006 0008 (2006)). Suitable examples of the yeast include standard budding yeast INVSc1 (invitrogen) and YPH499 (stratagene).
[0086] The expression vector into which the gene is applied is not particularly limited and may be a vector to be generally used. For example, when the host is E. coli, there are given ones derived from pUC18, pACYC184, and the like. When the host is Bacillus subtilis, there are given pUB110, pE194, pC194, pHY300PLK DNA, and the like. And when the host is yeast, there are given pRS303, YEp213, TOp2609, and the like.
[0087] Whether or not a gene of interest is introduced into the host cell may be confirmed by a conventional method such as a PCR method, a Southern hybridization method, or a northern hybridization method.
[0088] The production method for a C.sub.50 carotenoid of the present invention includes the step of culturing, in a medium, the cells as the transformants obtained as described above. The medium may be any medium containing a substance that may serve as a supply source for the C.sub.50 carotenoid backbone compound, and may be any medium containing an ingredient to be generally used for cell culturing. For cells in which the C.sub.50 carotenoid backbone compound is synthesized by the metabolism of IPP and DMAPP, the medium may be any medium containing a carbon source that may serve as a supply source for IPP and DMAPP. Examples of such carbon source include a variety of sugars such as glucose.
[0089] A temperature at the time of the culturing is not particularly limited but is set to preferably 18 to 30 C., more preferably 20 to 30 C.
[0090] Culture period is also not particularly limited but the culturing is performed for preferably 12 to 72 hours, more preferably 24 to 48 hours after the expression of the gene introduced by the transformation.
[0091] The C.sub.50 carotenoid can be collected from the culture after the culturing in accordance with a method to be generally employed for obtaining a product such as a carotenoid from cells of microorganisms or the like. It may also be possible to separate only the cells from the culture and obtain the carotenoid from the cells.
[0092] It should be noted that the present invention is also directed to a mutant phytoene desaturase gene, a mutant phytoene desaturase encoded by the mutant phytoene desaturase gene, and a cell capable of desaturating a C.sub.50 carotenoid backbone compound to produce a C.sub.50 carotenoid, which is transformed with the mutant phytoene desaturase gene.
[0093] Further, the present invention can be utilized in the highly efficient synthesis of a desaturated C.sub.55 carotenoid, a desaturated C.sub.60 carotenoid, or the like. For example, the desaturated C.sub.55 carotenoid as well as the C50 carotenoid can be produced with high efficiency by utilizing the present invention using a double mutant of a farnesyl diphosphate synthase (FDS) (FDS.sub.I78G,Y81A) in which isoleucine at position 78 is substituted by glycine (I78G) and tyrosine at position 81 is substituted by alanine (Y81A) in FDS (Ohnuma S et al., J Biol Chem 273, 26705-26713, 1998). Further, the desaturated C.sub.60 carotenoid can be produced with high efficiency by utilizing the present invention using a C.sub.30PP synthase (HexPS) derived from Micrococcus luteus (Shimizu N et al, J Bacteriol 180, 1578-1581, 1998), that is, by co-expressing FDS.sub.I78G,Y81A or HexPS with the CrtM variant.
EXAMPLES
[0094] Hereinafter, the present invention is specifically described by way of Examples. However, the present invention is by no means limited thereto.
(Reference Example 1) Synthesis of C.SUB.50 .Carotenoid Backbone Compound
[0095] (1) Supply of C.sub.50 Carotenoid Raw Material, C.sub.25PP
[0096] A mutant gene fds.sub.Y81A, V157A was used in order to efficiently synthesize C.sub.25PP in E. coli. fds.sub.Y81A, V157A is a mutant of a farnesyl diphosphate synthase (FDS) derived from Geobacillus stearothermophillus. The mutation Y81A is derived from Ohnuma, S. et al., J Biol Chem 271, 30748-30754 (1996). Further, the inventors of the present invention produced fds.sub.Y81A,V157A encoding a mutant enzyme having further shifted size specificity for a substrate by further introducing a mutation into a mutant gene fds.sub.Y81A through the use of the screening method for a terpene synthase gene disclosed in JP 2010-258989.
[0097] (2) Synthesis of C.sub.50 Carotenoid Backbone Compound
[0098] A mutant gene crtM.sub.F26A,W38A,233S was used for the synthesis of a C.sub.50 carotenoid backbone compound (16,16-diisopentenylphytoene) via the condensation of two molecules of C.sub.25PP. A diapophytoene synthase (CrtM) derived from Staphylococcus aureus is originally an enzyme that synthesizes a C.sub.30 backbone carotenoid via the condensation of two molecules of C.sub.15PP. The inventors of the present invention introduced a mutation into a crtM gene in order to produce an enzyme having improved size selectivity for a substrate (Umeno et al., J Bacteriol 184, 6690-6699 (2002), Umeno et al., Nucleic Acids Res 31, e91 (2003)). It was found that a C.sub.50 carotenoid backbone compound was synthesized in a trace amount by feeding C.sub.25PP to a double mutant of CrtM having mutations F26A and W38A (Non Patent Literature 7).
[0099] The inventors also found that a triple mutant of CrtM having introduced therein mutations F26A, W38A, and F233S synthesized a C.sub.50 carotenoid backbone compound from two molecules of C.sub.25PP in an extremely efficient manner, and synthesized a C.sub.60 carotenoid backbone compound, though in a trace amount, when C.sub.30PP was fed (Maiko Furubayashi, Mayu Ikezumi, Kyoichi Saito, Daisuke Umeno. Activity evolution of unnatural carotenoid synthetic pathways, Annual Meeting of the Kanto Branch of the Japan Society for Bioscience, Biotechnology, and Agrochemistry, 2010, Oct. 9, 2010: Daisuke Umeno, Maiko Furubayashi, Mayu Ikezumi, Akinori Katabami, Ling Li, Jun Kajiwara. Creation and development of unnatural biosynthetic pathways, The Third Annual Meeting of the Japanese Society for Cell Synthesis Research, Institute of Industrial Science, the University of Tokyo, Nov. 12, 2010: Furubayashi M, Saito K, Umeno D, In-laboratory genetic drift of carotenoid synthase and its evolution of size specificity. The international chemical congress of Pacific basin societies, Hawaii, USA, Dec. 17, 2010: Maiko Furubayashi, Mayu Ikezumi, Kyoichi Saito, Daisuke Umeno. Selective synthesis of unnatural carotenoid by combinatorial expression of enzyme mutant, Annual Meeting of the Japan Society for Bioscience, Biotechnology, and Agrochemistry, 2011, March 2011). It was found that C.sub.50-carotene (n=3), a C.sub.50 carotenoid backbone compound, was efficiently (about 61%) produced by co-expressing fds.sub.Y81A, V157A for supplying C.sub.25PP and crtM.sub.F26A,W38A,F233S in E. coli XL1-Blue.
[0100] (3) It should be noted that the transformation of E. coli XL1-Blue with fds.sub.Y81A, V157A and crtM.sub.F26A,W38A,F233S was performed by producing plasmids pAC-crtM.sub.F26A,W38A,F233S (
[0101] pAC-crtM.sub.F26A,W38A,F233S was produced by inserting lac promoter/operator (lacPO)-crtM.sub.F26A,W38A,F233S into the BamHI site of a pACmod vector (Claudia Schmidt-Dannert et al., Nat. Biotechnol., 18: 750-753 (2000)).
[0102] pUC-fds.sub.Y81A,V157A was produced by inserting an fds.sub.Y81A,V157A gene downstream of lacPO of a pUC18 Nm vector (Umeno D. et al, J Bacteriol 184, 6690-6699 (2002)).
[0103] The transformed E. coli was cultured in accordance with the technique disclosed in Non Patent Literature 7.
[0104] The analysis of the produced carotenoid was performed by HPLC also in accordance with the method disclosed in Non Patent Literature 7.
(Example 1) Improved Synthesis of C.SUB.50 .Carotenoid Backbone Compound
[0105] In addition to fds.sub.Y81A,V157A and CrtM.sub.F26A,W38A,F233S, a gene (derived from E. coli genome) encoding an isopentenyl diphosphate isomerase (Idi) was expressed in E. coli XL1-Blue, and the E. coli was cultured. The transformation of E. coli XL1-Blue with fds.sub.Y81A, V157A and crtM.sub.F26A,W38A,F233S was performed by producing plasmids pAC-crtM.sub.F26A,W38A,F233S-idi (
[0106]
(Reference Example 2) Desaturation of C.SUB.50 .Carotenoid Backbone Compound by Wild-Type CrtI
[0107] The inventors of the present invention found that a carotenoid having a C.sub.50 carotenoid backbone compound was desaturated by CrtI (phytoene desaturase encoded by a gene having a nucleotide sequence of SEQ ID NO: 2 (having introduced therein non-synonymous mutations G1131A and A1476T)) (Non Patent Literature 9). However, it was found that its production amount is extremely small and only 25% of the C.sub.50 carotenoid backbone compound was desaturated (Non Patent Literature 8).
[0108] Meanwhile, the inventors of the present invention found that the constitutive expression of wild-type CrtI using a lac promoter (lacP) or the like remarkably inhibited cell growth, and remarkably destabilized cell pigmentation. However, no clear cytotoxicity was observed in cells having a pathway to the synthesis/accumulation of the C.sub.50 carotenoid backbone compound (e.g., the cells obtained in Reference Example 1 and Example 1).
[0109] The inventors of the present invention attempted to ligate crtI downstream of an araBAD promoter capable of reducing leaky expression (low-level expression occurring without any induction) and express the ligation product in E. coli XL1-Blue. A group of carotenoid biosynthetic genes upstream of crtI were constitutively expressed by lacP. After the density/number of the cells had reached sufficient levels, it was attempted to make pigment in the cells by inducing the expression of crtI to desaturate the C.sub.50 carotenoid backbone compound.
[0110] The plasmid used is pUC-pBAD-crtI (having crtI introduced into the crtI variant part in
[0111] The problem of the cytotoxicity was overcome in E. coli transformed with pUC-pBAD-crtI. However, the C.sub.50 carotenoid backbone compound was desaturated with extremely low efficiency, which was almost unrecognizable.
(Example 2) Acquisition of crtI Variant Desaturating C.SUB.50 .Carotenoid Backbone Compound
[0112] Based on the evolutionary engineering of a phytoene desaturase (CrtI), it was attempted to acquire a crtI variant that desaturates more efficiently the C.sub.50 carotenoid backbone compound.
[0113] First, a plasmid pUC-pBAD-crtI containing wild-type crtI (represented by pUC-I in
[0114] E. coli XL1-Blue harboring a plasmid pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A (represented by pAC-C.sub.50 in
[0115] As a control, E. coli XL1-Blue was transformed with pUC-pBAD-crtI containing wild-type crtI. In this case, the colonies developed a flesh color. In the group of about 2,000 colonies obtained by transformation with the crtI variant plasmid library, 8 colonies developing a particularly intense reddish violet color were visually detected. The colonies were named CrtI-m1, m2, and m8, respectively. As illustrated in
[0116] The bacterial strain of each of the colonies was cultured in an LB liquid medium at 37 C. for 12 hours to extract a plasmid, and the nucleotide sequence of a crtI variant contained in the plasmid was analyzed by a dideoxy method. Table 1 below shows the analysis results.
TABLE-US-00001 TABLE 1 Analysis results of gene mutations in CrtI variants Gene mutations (amino acid mutations are Sample names shown in parentheses) CrtI-m1 A195G, A594G, T1016C (F339S) CrtI-m2 A911G (N304S) CrtI-m3 None CrtI-m4 T1015C (F339L), G1183A (D395N) CrtI-m5 None CrtI-m6 A682G (I228V), A1012G (I338V) CrtI-m7 T144C, A1012G (I338V) CrtI-m8 A911G (N304S), T1017C
[0117] It was found that CrtI-m2 and CrtI-m8 had the same mutation in which asparagine (N) at position 304 was substituted by serine (S) (N304S). Further, CrtI-m1 and CrtI-m4 each had a mutation in which phenylalanine (F) at position 339 was substituted by serine (S) or leucine (L) (F339S or F339L), and CrtI-m6 and CrtI-m7 each had a mutation in which isoleucine (I) at position 338 was substituted by valine (V) (I338V). It was estimated that the CrtI variants each had an enhanced ability to desaturate a C.sub.50 carotenoid backbone compound by virtue of those mutations.
(Example 3) Synthesis of Desaturated C.SUB.50 .Carotenoid by CrtI Variant
[0118] Of the colonies obtained in Example 2, each of CrtI-m1, m2, m4, m6, and m8, which showed enhanced pigmentation as compared to wild-type CrtI, was confirmed for its ability to desaturate a C.sub.50 carotenoid backbone compound.
[0119] E. coli XL1-Blue harboring pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A was transformed with each of the plasmids pUC-pBAD-CrtI-m1, m2, m4, m6, and m8. The transformant was spread on an LB agar medium on which a nitrocellulose (NC) membrane was contracted, and cultured at 37 C. for 24 hours. The plasmids pUC-pBAD-CrtI-m1, m2, m4, m6, and m8 have various mutant genes mut1, mut2, mut4, mut6, and mut8 inserted into the crtI* part in pUC-pBAD-crtI*-crtY of
[0120] After the formation of the colonies, the NC membrane with the colonies was transferred onto an LB agar medium containing 0.2% arabinose, followed by incubation at room temperature. The colonies were inoculated into 2 mL of an LB medium (containing 50 g/mL carbenicillin and 30 g/mL chloramphenicol) and cultured at 37 C. overnight. 300 L of the culture medium were inoculated into 30 mL of a TB medium (containing 50 g/mL carbenicillin and 30 g/mL chloramphenicol), followed by incubation under shaking at 30 C. and 200 rpm. After the incubation under shaking for 24 hours, 20% arabinose was added to the culture medium so as to have a final concentration of 0.2%, followed by incubation under shaking (30 C.) for an additional 48 hours.
[0121] The culture medium was measured for its OD.sub.600, and the cells were harvested by centrifugation. The pellet obtained by harvesting the cells was washed with physiological saline, and a lipid-soluble fraction was extracted with 10 mL of acetone. A 300-L aliquot was fractionated from the extract and measured for its absorbance spectrum with Spectra Max 384 (Molecular Device).
[0122]
[0123] Next, the carotenoid synthesized in the case of CrtI-m2 was subjected to HPLC analysis. 1 mL of hexane and 35 mL of 10% NaCl were added to the acetone extract to extract a carotenoid fraction into a hexane phase. 75% of the hexane extract were collected and dehydrated with addition of a small amount of MgSO.sub.4. The hexane solvent was removed by nitrogen, and the carotenoid fraction was finally concentrated into 100 L of hexane. Thus, a carotenoid extract was obtained. 25 L (75%25%=19% of the total volume, corresponding to 7.3 mL of the medium) of the resultant carotenoid extract were injected into an HPLC-photodiodearray system. HPLC analysis was performed in accordance with the conditions of Takaichi, S. Photosynth Res, 65, 93-99 (2000) (column: Waters Spherisorb 5.0 m ODS2 4.6 mm250 mm Column, eluent: acetonitrile/tetrahydrofuran/metanol (58:7:35) 2 mL/min, detector: photodiode array (190 to 800 nm)). Further, the mass spectrometry of a sample fractionated by HPLC was performed through the use of an M-2500 Hitachi double-focusing mass spectrometer (Hitachi, Ltd.) at a field desorption mode (Takaichi (1993) Org. Mass Spectrom. 28: 785-788)).
[0124] As a result, it was found that, in CrtI-m2, a compound (C.sub.50-lycopene) obtained by the six-step desaturation of the C.sub.50 carotenoid backbone compound was synthesized in a large amount (peak 3 in
[0125] The analysis results for peak 2 and peak 3 in
[0126] C.sub.50-lycopene (n=15): A sample corresponding to peak 3 in
(Example 4) Cyclization of Desaturated C.SUB.50 .Carotenoid
[0127] C.sub.50-lycopene (n=15), a desaturated C.sub.50 carotenoid, was cyclized by using a crtY gene encoding a lycopene cyclase, which synthesizes a -carotenoid from lycopene.
[0128] A plasmid pUC-pBAD-crtI/CrtI-m2-crtY was used for transformation with the crtY gene. The plasmid was produced by inserting an SpeI site following an ApaI site in pUC-pBAD-crtI/CrtI-m2 and inserting the crtY gene into the ApaI/SpeI site. The crtY gene is a gene encoding a lycopene cyclase derived from Pantoea ananatis (Misawa N. et al., J Bacteriol 172, 6704-6712 (1990)). It should be noted that the expression CrtI-m2 in the plasmid means that a mutant gene crtI.sub.N304S derived from CrtI-m2 has been inserted. The nucleotide sequence of pUC-pBAD-CrtI-m2-crtY is set forth in SEQ ID NO: 13.
[0129] E. coli XL1-Blue harboring pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A was transformed with pUC-CrtI-m2-CrtY. As a control, transformation was performed with crtY together with wild-type crtI in place of crtI-m2. The E. coli was spread on an LB agar medium on which a nitrocellulose (NC) membrane was mounted, and cultured at 37 C. for 24 hours. After the formation of colonies, the NC membrane with the colonies was transferred onto an LB agar medium containing 0.2% arabinose, followed by incubation at room temperature. Then, the color of the colonies was observed.
[0130]
[0131] Further, the acetone extract was subjected to HPLC analysis and mass spectrometry by the same techniques as those of Example 3.
[0132] A carotenoid having a maximum absorption peak at 502 nm was detected by the HPLC analysis (peak 7 in
[0133] C.sub.50--carotene: A sample corresponding to peak 7 in
(Example 5) Extension of Cyclic C.SUB.50 .Carotenoid Pathway by Additional Modification
[0134] An oxocarotenoid was synthesized by further extending the pathway for synthesizing a cyclic C.sub.50 carotenoid confirmed in Example 4.
[0135] pUC-pBAD-crtI-crtWZY (
[0136] As a result, in a system having introduced therein pUC-pBAD-CrtI-m2-crtWZY, the colonies developed a vivid red color (the second line from the right in
[0137] The spectrum of the acetone extract was measured in the same manner as in Example 4. As a result, in the case of transformation with pUC-pBAD-CrtI-m2-crtWZY, an intense peak appeared at 508 nm (CrtI*-CrtWZY in
(Example 6) Oxidation of Desaturated C.SUB.50 .Carotenoid
[0138] The total synthesis of crtA was performed by optimizing a codon for E. coli based on the amino acid sequence of CrtA derived from Rhodobacter sphearoides (SEQ ID NO: 7, commissioned to DNA2.0). Plasmids pUC-pBAD-crtI-crtA and pUC-pBAD-CrtI-m2-crtA were produced by using the synthesized gene (
[0139] By the same techniques as those of Example 5, E. coli was transformed with the produced plasmids, and the E. coli was cultured, followed by observing the color of colonies and analyzing the spectrum of the acetone extract.
[0140] As a result, in the case of transformation with pUC-pBAD-CrtI-m2-crtA, the colonies developed a vivid color (the first line from the right in
(Example 7) Acquisition of crtI Variant Having High Ability to Desaturate C.SUB.50 .Carotenoid Backbone Compound
[0141] The biosynthetic pathways for C50-lycopene and C50--carotene realized in Examples 3 and 4 left something to be improved in efficiency, because the C50 backbone (C50-carotene (n=3)) still remained. Thus, the acquisition of a CrtI variant having a higher ability to desaturate the C50 backbone was attempted. Of the CrtI variants obtained in Example 2, CrtI-m2 showed the highest C50 backbone desaturation efficiency. Thus, with attention focused on the amino acid substitution N304S of CrtI-m2, the site-directed total substitution of an amino acid at position 304 was performed to search a variant having higher desaturation efficiency.
[0142] First, a plasmid pUC-pBAD-crtI containing wild-type CrtI was used as a template, and a library was prepared by PCR using a primer having a randomized amino acid at position 304 (NNK codon) and the subsequent cloning. The resultant plasmid library was screened by the same method as that described in Example 2. Colonies developing a redder color than those of wild-type CrtI were searched to isolate plasmids of CrtI variants. Those CrtI variants were screened again. As a result, products substituted by glycine (G), serine (S), asparagine (N), proline (P), and alanine (A) gave particularly red colonies. Of those, a product substituted by P (codon: CCT) gave the reddest colonies. The amino acid sequence of CrtI having the product substituted by P is set forth in SEQ ID NO: 27 of the sequence listing, and a nucleotide sequence encoding the amino acid sequence is set forth in SEQ ID NO: 28.
[0143] Next, the synthesis amounts of C50-lycopene by CrtI-m2 and CrtI.sub.N304P were analyzed by HPLC. E. coli XL1-Blue was transformed with pUC-pBAD-crtI-m2 or pUC-pBAD-crtI.sub.N304P together with pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A. After the formation of colonies, an NC membrane with the colonies was transferred onto an LB agar medium containing 0.2% arabinose, followed by incubation at room temperature. The colonies were inoculated into 2 mL of an LB medium (containing 50 g/mL carbenicillin and 30 g/mL chrolamphenicol) and cultured at 37 C. overnight. 300 L of the culture medium were inoculated into 30 mL of a TB medium (containing 50 g/mL carbenicillin and 30 g/mL chrolamphenicol), followed by incubation under shaking at 30 C. and 200 rpm. After the incubation under shaking for 36 hours, 20% arabinose was added to the culture medium so as to have a final concentration of 0.20, followed by incubation under shaking (30 C.) for an additional 36 hours. HPLC analysis was performed by the method shown in Example 3.
[0144]
[0145] Next, whether or not C50--carotene was increased more by using CrtI.sub.N304P was investigated. First, a pUC-pBAD-crtI.sub.N304P-crtY plasmid was prepared. E. coli XL1-Blue was transformed with the plasmid and pUC-pBAD-crtI-m2-crtY together with pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A, and culturing, extraction, and HPLC analysis were performed in the same manner as in the above-mentioned sections.
[0146] As a result, C50-carotene (n=3) was decreased and C50-lycopene was increased in the case of using CrtI.sub.N304P as compared to the case of using CrtI-m2 (
(Example 8) Study on Use of CrtW and CrtZ Derived from Brevundimonas sp. Strain SD-212
[0147] In Example 5, it was attempted to produce C50-astaxanthin, in addition to C50--carotene, by the use of CrtW and CrtZ derived from Paracoccus sp. strain N81106. A polar peak appeared, but most of C50--carotene remained without any modification by CrtW or CrtZ. Thus, the synthesis of C50-astaxanthin and its intermediates C50-zeaxanthin and C50-canthaxanthin was attempted by the use of CrtW and CrtZ having higher efficiency.
[0148] As previously reported (Choi S. et al., Mar Biotechnol 7, 515-522 (2005), Choi S. et al., Appl Microbiol Biotechnol 72, 1238-1246 (2006)), it has been found that CrtW and CrtZ derived from Brevundimonas sp. strain SD-212 are a -carotene ketolase and -carotene hydroxylase having high efficiency, respectively. In the synthesis of a natural (C40 type) astaxanthin, the enzymes are the best choices that are currently available. Thus, the total synthesis of those genes was performed with codon optimization for E. coli, which was commissioned to DNA2.0. Through the use of those genes, pUC-pBAD-CrtI.sub.N304P-CrtY-CrtW.sub.BD-CrtZ.sub.BD was prepared. Further, pUC-pBAD-CrtI-m2-CrtY-CrtW.sub.BD and pUC-pBAD-CrtI-m2-CrtY-CrtZ.sub.BD were also prepared. The plasmid maps of pUC-pBAD-CrtI-m2-CrtY-CrtW.sub.BD, pUC-pBAD-CrtI-m2-CrtY-CrtZ.sub.BD, and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtW.sub.BD-CrtZ.sub.BD are illustrated in
[0149] Those plasmids were introduced into E. coli (XL1-Blue) together with pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A, and culturing and extraction were performed by the method shown in Example 3. The obtained carotenoid extracts were each injected into an HPLC-photodiodearray system. Analysis was performed at a flow rate of 1 mL/min by using a Bondapak column (1008 mm, RCM-type, Waters) as a column and using methanol as an eluent.
[0150] As a result, C50-zeaxanthin was specifically synthesized in pUC-pBAD-CrtI-m2-CrtY-CrtZ.sub.BD (panel a in
(Example 9) Increase in C50-Astaxanthin Amount by Co-Expression of Idi
[0151] C50-astaxanthin was synthesized in E. coli by the method described in Example 8 using pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtW.sub.BD-CrtZ.sub.BD, and a synthesis amount thereof was determined from an HPLC peak area thereof.
[0152] As a result, C50-astaxanthin was synthesized at 288 g/gDCW (
[0153] In order to co-express idi therewith, pAC-crtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A-idi was prepared and transformed into E. coli (XL1-Blue) together with pUC-pBAD-CrtI.sub.N304P-CrtY-CrtW.sub.BD-CrtZ.sub.BD. Then, a carotenoid synthesis amount was determined by a similar method. The plasmid map of pAC-CrtM.sub.F26A,W38A,F233S-fds.sub.Y81A,V157A-idi is illustrated in
[0154] As a result, C50-astaxanthin was synthesized at 884 g/gDCW (
Example 10
[0155] A compound in the peak of C50--carotene obtained in Example 4 (peak 7 in
[0156] The maximum absorption wavelengths of the compound in the peak (peak 7 in
[0157] The compound in the peak (peak 3 in
[0158] The compound in the peak (peak 1 in
[0159] The compound in the peak (peak 2 in
(Example 11) Production of Carotenoids Having Great Variety of Structures by Additional Expression of CrtG and CrtX
[0160] A study on the diversification of carotenoid structures to be synthesized was made by the additional expression of a crtG gene derived from Brevundimonas sp. strain SD-212 (Nishida, Y. et al, Appl Environ Microbiol 71, 4286-4296, 2005) and a crtX gene derived from Pantoea ananatis. The crtX gene is a gene encoding a zeaxanthin glucosyl transferase.
[0161] First, pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtZ.sub.BD and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtW.sub.BD-CrtZ.sub.BD were prepared by using the crtG gene derived from Brevundimonas sp. strain SD-212. The plasmid maps of pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtZ.sub.BD and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtW.sub.BD-CrtZ.sub.BD are illustrated in
[0162] In the case of culturing E. coli co-expressing pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtZ.sub.BD and pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A, C.sub.50-caloxanthin and C.sub.50-nostoxanthin, which are hydroxylated zeaxanthin at the 2-position and 2-position, can be synthesized (
[0163] In the case of culturing E. coli co-expressing pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtW.sub.BD-CrtZ.sub.BD and pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A, C.sub.50-2-hydroxyastaxanthin and C.sub.50-2,3,2,3-tetrahydroxy-,-carotene-4,4-dione, which are hydroxylated astaxanthin at the 2-position and 2-position, can be synthesized (
[0164] Further, it is also possible to synthesize C.sub.50-2-hydroxycanthaxanthin and C.sub.50-2,2-dihidroxycanthaxanthin, which are hydroxylated canthaxanthin at the 2-position and 2-position (
[0165] Next, pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtZ.sub.BD and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtW.sub.BD-CrtZ.sub.BD were prepared by using the crtX gene derived from Pantoea ananatis. The plasmid maps of pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtZ.sub.BD and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtW.sub.BD-CrtZ.sub.BD are illustrated in
[0166] In the case of culturing E. coli co-expressing pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtZ.sub.BD and pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A, C.sub.50-zeaxanthin--D-glucoside and C.sub.50-zeaxanthin--D-diglucoside, which are glycosidated zeaxanthin at the hydroxyl groups at the 3-position and 3-position, can be synthesized (
[0167] In the case of culturing E. coli co-expressing pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtW.sub.BD-CrtZ.sub.BD and pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A, C.sub.50-astaxanthin--D-glucoside and C.sub.50-astaxanthin--D-diglucoside, which are glycosidated astaxanthin at the hydroxyl groups at the 3-position and 3-position, can be synthesized (
[0168] In fact, when E. coli (XL1-Blue) co-expressing any one of pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtZ.sub.BD, pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtZ.sub.BD, pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtW-CrtZ.sub.BD, and pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtW.sub.BD-CrtZ.sub.BD together with pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A was spread on an LB solid medium to form colonies, the formed colonies developed a reddish violet color (
[0169] The colonies were inoculated into 2 mL of an LB liquid medium and cultured for 16 hours. After that, the culture medium was inoculated into 30 mL of a TB liquid medium in a 1/100 volume with respect to the TB liquid medium. After incubation under rotation at 200 rpm at 30 C. for 36 hours, L-arabinose was added so as to have a final concentration of 0.2% (v/v), followed by incubation for an additional 36 hours. The cells were harvested and collected from 2 mL of the culture medium and washed with physiological saline, and then a carotenoid fraction was extracted with the addition of 1 mL of acetone.
[0170] Next, E. coli (XL1-Blue) was transformed with pUC-pBAD-CrtI.sub.N304P-CrtY-CrtX-CrtZ.sub.BD or pUC-pBAD-CrtI.sub.N304P-CrtY-CrtG-CrtZ.sub.BD and pAC-CrtM.sub.F26A,W38A,F233S-FDS.sub.Y81A,V157A. The cell colonies were inoculated into 2 mL of an LB liquid medium and cultured for 16 hours. After that, the culture medium was inoculated into 30 mL of a TB liquid medium in a 1/100 volume with respect to the TB liquid medium. After incubation under rotation at 200 rpm at 30 C. for 36 hours, L-arabinose was added so as to have a final concentration of 0.2% (v/v), followed by incubation for an additional 36 hours. The cells were harvested by centrifuging the culture medium and washed with physiological saline. 10 mL of acetone were added to the cell pellet to extract a carotenoid fraction. 1 mL of chloroform and 35 mL of 10% NaCl were added to the acetone extract to extract the carotenoid fraction into a chloroform phase. All the chloroform extracts were collected and dehydrated with the addition of MgSO.sub.4. The chloroform solvent was eliminated by nitrogen, and the carotenoid fraction was finally concentrated into 100 L of methanol/THF (1:1, v/v). Thus, a carotenoid extract was obtained. 10 L (10% of the total volume, corresponding to 3 mL of the medium) of the obtained carotenoid extract were injected into an HPLC-photodiodearray system. HPLC analysis was performed in accordance with the conditions of Nishida, Y. et al, Appl Environ Microbiol, 71, 4286-4296 (2005) (column: TSK gel ODS-80 Ts column (4.6-mm inner diameter by 150 mm; Tosoh Co.), eluent: Eluent A (methanol/water, 95:5) for 5 minutes, Eluent A to Eluent B (methanol/tetrahydrofuran, 7:3) for 5 minutes, Eluent B for 15 minutes, 1 mL/min, detector: photodiode array (190 to 800 nm)).
[0171] As a result, in the case of co-expression of CrtX with C50-zeaxanthin, one new peak appeared at a shorter elution time (peak in
[0172] Further, in the case of co-expression of CrtG with C50-zeaxanthin, two new peaks appeared (peaks 2 and 3 in
(Example 12) Biosynthesis of C.SUB.55 .and C.SUB.60 .Carotenoids
[0173] A mutant FDS having introduced therein mutations I78G and Y81A (FDS.sub.I78G,Y81A) synthesizes C.sub.25PP and a prenyl diphosphate (e.g., C.sub.30PP or C.sub.35PP) which is a resultant of further addition of C.sub.5 unit(s) to C.sub.25PP (Ohnuma S et al., J Biol Chem 273, 26705-26713, 1998). Further, a C.sub.30PP synthase (HexPS) derived from Micrococcus luteus synthesizes C.sub.30PP (Shimizu N et al, J Bacteriol 180, 1578-1581, 1998). The biosynthesis of a larger carotenoid backbone than a C.sub.50 backbone was attempted by co-expressing FDS.sub.I78G,Y81A or HexPS with a CrtM variant.
[0174] First, pAC-hexPS, pAC-FDS.sub.I78G,Y81A-idi, and pUC-CrtM.sub.F26A,W38A,F233S were prepared. The plasmid maps of pAC-hexPS, pAC-FDS.sub.I78G,Y81A-idi, and pUC-CrtM.sub.F26A,W38A,F233S are illustrated in
[0175] E. coli (XL1-Blue) was transformed with pAC-FDS.sub.I78G,Y81A-idi or pAC-hexPS together with pUC-CrtM.sub.F26A,W38A or pUC-CrtM.sub.F26A,W38A,F233S. The culturing of the cells and the analysis of the produced carotenoid were performed in the same manner as in Reference Example 1.
[0176]
[0177] Next, pAC-FDS.sub.I78G,Y81A-idi or pAC-hexPS was co-expressed with 8 kinds of CrtM variants (pUC-CrtM variants), and carotenoid synthesis amounts thereof were investigated by a similar method.
INDUSTRIAL APPLICABILITY
[0178] As described above, the production method of the present invention can synthesize the desaturated C.sub.50 carotenoid in an extremely efficient manner, and allows various C.sub.H carotenoids to be synthesized. The C.sub.50 carotenoid is rarely found in nature, and it is not too much to say that there is no synthesis example thereof. Carotenoids are known to have physiological activities such as an antioxidant action. Of those, the C.sub.50 carotenoid is expected to exhibit unprecedented novel actions and to have remarkably enhanced activities as compared to conventional carotenoids. For example, the C.sub.50 carotenoid is expected to have the potentiality of having a high antioxidant activity, an application as a novel seed for a physiologically active substance having an antitumor activity or the like, and a use as a functional pigment molecule. Further, the production method of the present invention may be utilized in the highly efficient synthesis of the desaturated C.sub.55 carotenoid, the desaturated C.sub.60 carotenoid, and the like. In addition, the production method of the present invention is considered to drastically increase variety of synthesizable carotenoids, by being used in combination with related art such as cells having an enhanced isoprenoid synthetic pathway (Klein-Marcuschamer D et al.: Trends Biotechnol 25, 417-424 (2007), Kirby J et al.: Nat Prod Rep 25, 656-661 (2008)).