Patent Application
20240093253
Research and therapeutic use of phytocannabinoids, which are compounds originally isolated from the plant Cannabis. sativa, has been largely hindered due to legal and social issues. Some cannabinoids such as Δ9-tetrahydrocannabinol (THC), produced as a mixture with other cannabinoids in the plant, are found to be psychoactive. However, there are at least 113 known cannabinoids isolated from C. sativa (Aizpurua-Olaizola et al., J. Nat. Prod., 2016, 79(2):324-331), most of which are non-psychoactive and have distinct pharmacological properties.
The widespread expression of human cannabinoid receptors implies that these chemical compounds have an extensive effect on the human body. There are two main classes of receptors—CB1 receptors are expressed mainly in the central nervous system, while CB2 receptors are found predominantly in the peripheral immune system. In addition, studies have also uncovered expression of these receptors in various human tissues such as the heart, adrenal gland, lung, spleen, and tonsils (Galiègue et al., Eur. J. Biochem., 1995, 232(1):54-61). The association of cannabinoids with these receptors actuates signaling pathways that can potentially affect a wide range of biological systems in the human body.
Phytocannabinoids have been approved for use clinically by the US Food and Drug Administration as anti-emetic agents for patients undergoing intensive chemotherapy cancer treatment (THC and Dronabinol; Pertwee, Forsch. Komplementarmed., 1999, Suppl 3:12-15) and in the United Kingdom as a highly effective treatment for spasticity in patients with multiple sclerosis who are non-responsive to other medications (Flachenecker et al, Eur. Neurol., 2014, 71(5-6):271-279). Various studies have also shown the therapeutic potential of phytocannabinoids as anti-tumor agents (Velasco et al., Nat. Rev. Cancer, 2012, 12(6):436-444; Maria Pyszniak et al., Onco. Targets Therapy, 2016,.9:4323-4336) and anti-bacterial agents that may be effective against several strains of methicillin-resistant Staphylococcus aureus (MRSA) (Appendino et al., J. Nat. Prod., 2008, 71(8):1427-1430).
In light of these recent developments in cannabinoid research, the legal cannabis market is currently estimated to be worth USD7.7 billion internationally and this is expected to grow to around USD31.4 billion by 2021 (Zhang, Forbes, 2017).
Currently, most of the cannabinoids for research or therapeutic use are produced from C. sativa extracts. Legal and social implications associated with the illicit use of the plant extracts poses the greatest challenge faced by traditional cultivation due to the high concentrations of psychoactive components such as THC, produced as a mixture in C. sativa. There is limited control in the selectivity of cannabinoids that are produced in the cultivation of C. sativa. Furthermore, there is a huge gap in the market for C. sativa strains producing minor cannabinoids such as cannabidivarin (CBDV) and cannabicyclol (CBL) for research into their therapeutic potential.
The cultivation of these plants is not only expensive due to the need for highly energy-intensive processes to control environmental factors, it is also environmentally unsustainable. Research conducted in 2012 by the Energy & Resources group in the Lawrence Berkeley National Laboratory estimated that the cost of energy consumption from the indoor practice of cannabis cultivation in the US alone was around USD 6 billion annually. Further, greenhouse gas emissions from this practice to produce a kilogram of the final product is equivalent to that of 3 million cars (Mills, Energy Policy, 2012, 46:58-67).
There exists a need to find alternative means of cannabinoid production that circumvents the complications described above.
To meet the need set out, supra, a recombinant cell of Saccharomyces cerevisiae is provided that contains in its genome a plurality of nucleic acids each encoding a cannabinoid biosynthetic pathway gene such that a cannabinoid is produced by the recombinant cell in the presence of a cannabinoid precursor substrate. At least one of the cannabinoid biosynthetic pathway genes is not from Cannabis sativa.
Also disclosed is a method for producing a cannabinoid by contacting the recombinant cell with a cannabinoid precursor substrate and culturing the recombinant cell.
The details of one or more embodiments are set forth in the description and the examples below. Other features, objects, and advantages will be apparent from the detailed description, from the drawings, and also from the appended claims.
The invention description below refers to the accompanying drawings, of which:
As summarized above, the recombinant cell provided contains in its genome a plurality of nucleic acids each encoding a cannabinoid biosynthetic pathway gene. In an exemplary recombinant cell, the cannabinoid biosynthetic pathway genes are from organisms other than Cannabis sativa.
Certain recombinant cells encompassed by the invention contain a nucleic acid that encodes a coenzyme A (CoA) ligase. The CoA ligase can be, but is not limited to, Nicotiana tabacum 4-coumaryl-CoA ligase (SEQ ID NO: 1), Rhodopseudomonas palstri benzoate-CoA ligase (SEQ ID NO: 2), and Streptomyces coelicolor phenylacetate-CoA ligase (SEQ ID NO: 3). The CoA ligase can have 70% or greater identity (e.g., 70%, 75%, 80%, 85%, 90%, 95%, and 99% or greater) to the above-mentioned sequences while retaining enzymatic activity.
Further, the recombinant cell can include nucleic acids encoding each of an a malonyl-CoA synthethase (MCS), an olivetol synthase (OLS), and an olivetolic acid cyclase (OAC). In particular recombinant cells, the MCS is replaced by an acyl-activating enzyme (AAE).
The MCS can have the amino acid sequence of SEQ ID NO: 5, the OLS can have the amino acid sequence of SEQ ID NO: 6, the OAC can have the amino acid sequence of SEQ ID NO: 7, and the AAE can have the amino acid sequence of SEQ ID NO: 4.
Alternatively, the MCS, OLS, OAC, and AAE can have an amino acid sequence having 70% or more identity to the amino acid sequence of their corresponding SEQ ID NOs.
The recombinant cell set forth above will produce a cannabinoid in the presence of a cannabinoid precursor substrate. The cannabinoid precursor substrate can be, e.g., butyric acid, valeric acid, hexanoic acid, heptanoic acid, and octanoic acid. Additional cannabinoid precursor substrates are shown in Table 1 below.
As set forth in the SUMMARY section, a method for producing a cannabinoid is disclosed that uses the recombinant cell described above. The method is carried out by contacting the recombinant cell with a cannabinoid precursor substrate and culturing the recombinant cell.
In an exemplary method, the recombinant cell expresses a CoA ligase, a malonyl-CoA synthethase, an olivetol synthase, and an olivetolic acid cyclase, and the cannabinoid precursor substrate is butyric acid, valeric acid, hexanoic acid, heptanoic acid, or octanoic acid. Additional cannabinoid precursor substrates shown above in Table 1 can also be used in this method.
The cannabinoid biosynthetic pathway reconstituted synthetically in micro-organisms such as Saccharomyces cerevisiae is used for bio-production of major and minor cannabinoids. This method of bio-production facilitates the production of specific cannabinoids of interest, as compared to the mixture of cannabinoids produced by cultivation of C. sativa. Further, minor cannabinoids can be produced with high yield. In addition, enzymes in the cannabinoid biosynthetic pathway can be manipulated and expressed in micro-organisms to produce novel and unique cannabinoids that have therapeutic potential.
Without further elaboration, it is believed that one skilled in the art can, based on the disclosure herein, utilize the present disclosure to its fullest extent. The following specific examples are, therefore, to be construed as merely descriptive, and not limitative of the remainder of the disclosure in any way whatsoever. All publications cited herein are incorporated by reference in their entirety.
To reconstruct the cannabinoid biosynthetic pathway in micro-organisms, it is necessary to first understand the enzymes present in C. sativa that catalyze each step in the pathway. See
The upstream biosynthetic pathway can be categorized into two functional parts, the polyketide pathway, producing olivetolic acid (OLA) as the final product and the isoprenoid pathway producing geranyl pyrophosphate (GPP).
The polyketide pathway (see
In C. sativa, isoprenoids such as dimethylallyl-pyrophosphate (DMAPP) and isopentenyl-pyrophosphate (IPP) are produced through the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway (see
Isoprenoids can also be produced in nature through the mevalonate pathway more commonly present in micro-organisms such as yeast and some bacteria (Buhaescu et al., Clin. Biochem., 2007, 40(9-10):575-584).
Once OLA and GPP are produced, the aromatic prenyltransferase enzyme geranylpyrophosphate:olivetolate geranyltransferase (GOT) then catalyzes the production of the first cannabinoid, cannabigerolic acid (CBGA), by transferring the C10 prenyl group in GPP onto C3 of olivetolic acid (Fellermeier et al., FEBS Lett., 1998, 427(2):283-285; see
Modifications made to the cannabinoid biosynthetic pathway are illustrated in green in
Each CoA-ligase is paired with malonyl-CoA synthethase (MCS), which is responsible for adding the CoA-moiety onto malonic acid.
It is challenging to express the prenyltransferase from C. sativa, i.e., GOT, in a heterologous system. Indeed, this enzyme is predicted to be a membrane-associated protein with intrinsic trans-membrane regions, as shown by the bioinformatics prediction tool, TMHMM (Carvalho et al., FEMS Yeast Res., 2017, 17(4)). See
A soluble prenyltransferase from Streptomyces sp., namely, NphB, was previously shown to be able to accept OLA as its prenyl-acceptor in bacterial systems such as E. coli (Kuzuyama et al., Nature, 2005, 435(7044):983-987; Yang et al., Biochemistry, 2012, 51(12):2606-2618). This enzyme was used as an alternative to GOT for heterologous expression of prenyl-transferases in the cannabinoid biosynthetic pathway.
The molecular cloning strategy for construct building in S. cerevisiae is a Golden-Gate assembly based suite of plasmids known as the YeastFab system (Guo et al.). The assembly system allows for the modular assembly of transcriptional units such as promoters and terminators to open reading frames (ORF), followed by the assembly of expression cassettes of up to six different transcriptional units.
The suite of YeastFab plasmids has been expanded to allow for the assembly of up to eight transcriptional units together. The modular nature of assembly advantageously facilitates downstream optimization due to the relative ease in changing out transcriptional regulatory units such as promoters and terminators to regulate the expression of each gene differentially in the biosynthetic pathway. In this method of pathway assembly, Type IIS restriction enzymes (e.g., BsaI and BsmBI) cuts adjacent to the enzyme recognition site, allowing both restriction enzymes and DNA ligase to work in a one-pot digestion-ligation reaction. See
Standard biological parts such as promoters, open reading frames and terminators are individually cloned into individual plasmids (Level 0). After the first round of one-pot digestion-ligation reaction, they are assembled into individual transcriptional units called POTs (Level 1). Each POT is designed to then assemble with another POT in the following reaction to assemble up to eight transcription units together into a pathway (Level 2) through prefix and suffix sequences that aligns together as depicted in
A library of yeast constitutive promoters was previously characterized according to their relative strengths. A set of promoters and terminators with various strength were chosen to express each enzyme in the biosynthetic pathway, reflecting their relative stoichometries and toxicities to the expression host. Different promoters and terminators were assigned for each ORF (see Table 2 below) to prevent homologous recombination that occurs frequently in yeast between homologous sequences that are close to each other (Orr-Weaver et al., Proc. Natl. Acad. Sci. USA, 1981, 78(10):6354-6358).
After assembly of the transcriptional units with the assigned promoters and terminators, they were assembled into a pathway with multiple genes in a single plasmid. In yeast, farnesyl pyrophosphate (FPP), which is a C15 version of GPP by adding an additional IPP to GPP, is endogenously produced by the enzyme Erg20p. Previous studies have shown that expressing a double mutant of the enzyme, i.e., Erg20pWW (F96W-N127W), increases endogenous GPP levels (Ignea et al., ACS Synth. Biol., 2014, 3(5):298-306). This double mutant, together with the geranyl diphosphate synthase (Ag-GPPase) from Abies grandis (Burke et al., Arch. Biochem. Biophys., 2002, 405(1):130-136) and a chimeric GPP synthase (Chi-GPPase), were used to produce GPP in the construct to feed the reaction forward.
After assembly of expression genes into their intended plasmids, they were then transformed into a single organism (S. cerevisiae) for bioproduction of the intended product. The yeast strain BY4741, which is auxotrophic for the amino acids methionine, leucine, histidine and uracil (Brachmann et al., Yeast, 1998, 14(2):115-132), was used for bio-production of cannabinoids. A step-wise approach can be taken as precautionary measure to ensure that yeast transformed with each plasmid subsequently expresses a functional enzyme. The product of each step (e.g., OLA, CBGA, and CBDA) was then detected using liquid chromatography—mass spectrometry (LC-MS) before moving on to the next step in the biosynthesis pathway. S. cerevisiae cultures were grown to stationary phase to express the enzymes.
Substrates, i.e., hexanoic acid and malonic acid, were added to the cultures, which were then incubated overnight at 25° C. Cultures were spun down to separate the pellets from the supernatant media. Both the cell pellets and supernatant media were checked for the presence of the intended product by LC-MS.
To prepare samples for LC-MS analysis, the supernatant media was acidified to pH<2.0 before extracting it three times with ethyl acetate. The extracted ethyl acetate was dried using a rotary vacuum concentrator, resuspended in methanol, and analysed by LC-MS. The cell pellets were also checked for presence of the intended product by firstly lysing the cells via glass-bead physical shearing or by chemical lysis. Consequently, the lysate underwent similar steps of acidification, organic extraction and LC-MS analysis.
Diversification of the cannabinoid library can be carried out to produce novel and unnatural cannabinoids by three different approaches, informed by computational analysis.
First, the traditional approach of precursor-directed combinatorial biosynthesis involving the utilization of different substrates fed to the constructs will facilitate the exploration of substrate-promiscuity profiles of the enzymes in the pathway. Unique and novel products formed at each step then serve as new substrates for the next step in the pathway, hence increasing the diversity of products produced. Each enzyme has an innate specificity to its substrates that it can accept due to steric constraints and interactions in its binding pocket. Computational approaches such as in silico docking allows the screening of large libraries of small-molecule compounds in a high-throughput manner to identify substrates with a favorable binding affinity that is then tested experimentally.
Second, in silico docking of a substrate to the enzyme structure will clearly elucidate the spatial constraints and the interactions of the substrate in the microenvironment of the active site. This information is then used to direct protein engineering. It is vital to understand the key interactions of the substrate to the binding pocket of the enzyme in order to rationally design specific mutations that may increase the diversity of substrates that each enzyme may accept.
Finally, there is a limit to the degree of protein engineering that can be applied to each enzyme as mutations thus introduced may unintentionally change the architecture of the entire protein structure and result in protein instability and inactivity. Orthologues from different organisms of the enzymes carrying out each biosynthetic step can be identified and incorporated into the pathway. The Enzyme Similarity tool from the Enzyme-Function Initiative (EFI-EST) is a bioinformatics web server that aids in the identification of orthologues of a protein query sequence (Gerlt et al., Biochim. Biophys. Acta, 2015, 1854(8):1019-1037). The web tool uses the UniProt database to identify amino acid sequences in nature that are related to the query sequence in terms of function and reactions catalyzed. It facilitates the visualization of their relationships by generating a sequence similarity network that identifies proteins from diverse families which may have very different substrate-specificity profiles. The orthologues thus identified, having an entirely different set of substrates that it can act on, can serve as suitable replacements for particular steps in the cannabinoid biosynthesis pathway and consequently produce unique and novel cannabinoid products.
Transcriptional units were assembled into POTs as described above in Example 2. The plasmids were inserted into the level 2 assembly plasmids, pCKU and pMKU, which contain, respectively, the yeast low or high copy origins of replication CEN and 2 μ, as well as a URA3 selection marker. The assembled plasmids were transformed into individual strains of S. cerevisiae BY4741 using a previously described lithium acetate method (Gietz et al., Nat. Protoc., 2007, 2(1):35-37). These strains were grown overnight before substrates hexanoic acid and malonic acid were added to the cultures. After an overnight incubation at 25° C. with the substrates, cultures were harvested and growth media from each culture was extracted with ethyl acetate. The results are shown in
Culture supernatants of yeast expressing four enzymes in the cannabinoid pathway, i.e., CoA ligase, MCS, OLS, and OAC, demonstrated a peak eluting at ˜4 min. having a m/z value of 223.100 (ppm error of 11.7), corresponding to that of an OLA. See
The next step in the pathway produces CBGA. To do so, the first four genes mentioned above that produce OLA were assembled together with a GPP synthase enzyme (Erg20pWW, AgGPPase, or ChiGPPase) and a prenyltransferase, i.e., GOT or NphB, into the level 2 assembly plasmid pCKU and pMKU. After assembly of the transcriptional units and transformation into the host yeast strains, culture supernatants were analyzed by LC-MS as described above. A CBGA product was not observed in all of the constructs assembled, intracellularly or extracellularly. Not to be bound by theory, it is possible that the lack of CBGA in some cultures resulted from poor enzyme expression of the prenyltransferases (GOT or NphB) or a lack of substrate (OLA or GPP) available for the reaction.
To test the activity of the prenyltransferase enzyme, level 1 POT plasmids expressing the transcriptional units of GOT and NphB prenyltransferase were separately transformed into BY4741 cells. The cultures were grown and lysed at stationary phase as described above. An aliquot of the lysate was then added separately into an in vitro enzymatic assay set up with substrates OLA and GPP. A negative control was also set up by replacing the lysate with water. After incubation at 30° C., acidification and organic extraction was done before LC-MS detection. The results are shown in
A small peak corresponding to CBGA was observed in the negative control (without enzymes added) and the lysate containing GOT. See
NphB-containing lysate, on the other hand, showed a peak area for CBGA larger than to that of the negative control, indicating that the NphB was active. See
Methods for overexpressing monoterpenes derived from GPP in S. cerevisiae are well known in the art. There are an abundance of papers published describing work done in achieving improved monoterpene production in yeast due to their high commercial value. One approach to improve GPP yield is to reduce the metabolic burdens borne by the yeast host. It has been reported that, by overexpressing four genes involved in the mevalonate pathway and the respective monoterpene synthase, geraniol synthase, a seven-fold increase in geraniol yield was achieved, compared to previously engineered yeast strains (Zhao et al.).
Referring to
The IDI1, tHMG1, and UPC2-1 genes were assembled together with the previously described GPP synthase, Erg20pWW, using the YeastFab system as described above into level 1 POTs and subsequently into a level 2 assembly plasmid (pCKL/pMKL) expressing auxotrophic marker LEU2. This allows the expression of genes for cannabinoids and isoprenoids to be maintained on separate plasmids in order to reduce the length of each plasmids assembled and transformed into the yeast strains.
A series of medium to strong promoters and terminators were individually assigned to overexpress the four genes for GPP production maintained on the pCKL/pMKL plasmid using the leucine auxotrophic marker (LEU2), while a different set of promoters and terminators were assigned to enzymes in the cannabinoid genes, maintained on a separate plasmid, pCKU/pMKU. See Table 3 below.
After assembly of both cannabinoid (pCKU/pMKU) and mevalonate genes was achieved, both plasmids were then transformed into the yeast strain BY4741 and grown in media lacking both uracil and leucine to select for transformants. The same bio-production procedure was carried out with constructs expressing both plasmids. Trace amounts of CBGA was detected intracellularly after conducting organic extraction of the lysed cell pellets. The results are shown in
To further increase yields of CBGA produced by the pathway expressed in yeast, computational protein engineering was conducted on wild-type NphB to improve its selectivity in producing CBGA instead of the side product, 2-O-geranyl olivetolic acid. Four mutants, i.e., V49W/Y288A (SEQ ID NO: 8), V49W/Y288P (SEQ ID NO: 9), V49W/Y288A/Q295F (SEQ ID NO: 10), and V49W/Y288P/Q295F (SEQ ID NO: 11) were generated that are highly specific in prenylating olivetolic acid using the geranyl moiety from GPP at the correct site to produce CBGA. These 5 mutants, which showed a significant increase in CBGA yield while producing no side products at all, were subsequently integrated into the pathway and CBGA titers improved significantly in vivo.
Branch-points in the cannabinoid biosynthetic pathway can be exploited to produce novel cannabinoid compounds. The promiscuous nature of the acyl-CoA ligase and polyketide synthase, i.e., OLS, used in the above constructs allows for the use of different short-medium chain fatty acids (C3-C10) as substrates instead of hexanoic acid (C6) to produce analogues of olivetolic acid. An example in C. sativa is the production of the cannabinoids tetrahydrocannabivarin (THCV) and cannabidivarinic acid (CBDVA), which are both produced by the same enzymes in the pathway. These cannabinoids, produced in minor quantities, use the polyketide precursor divarinic acid (DVA) instead of OLA. DVA, which has a C3 chain-length on C2 of the aromatic ring instead of a C5 chain in OLA (see
OLS and OAC were tested for substrate-promiscuity by using different starter units (C3-C10) instead of hexanoic acid (C6). The results are shown in
Certain OLA analogues, i.e., (C3, C9, C10), were not produced in S. cerevisiae but were produced using the same biosynthetic pathway constructs in E. coli. See
The traditional method of precursor-directed combinatorial biosynthesis involves laborious screening of large libraries of substrates experimentally to detect if a new product was formed. In order to shorten the time and resources taken to identify favorable substrates, computational methods such as docking are employed as a prediction model to identify substrates that are able to fit into the binding pocket of the enzyme and that have favorable binding affinity to the active site. This facilitates screening of thousands of substrate libraries in a high-throughput manner to produce a ranked list of the most favorable substrates for experimental testing.
Starting with a 2.2 Å resolution structure of OLS, the native substrates of this enzyme, hexanoyl-CoA and malonyl-CoA were first docked to serve as a positive control. OLS uses two substrates with different R-groups, shuttled by a CoA moiety into the active site; a hexanoyl-CoA starter unit and three malonyl-CoA extender units that iteratively extends the starter unit by attaching acetyl-ketone groups onto the hexanoyl-intermediate attached to Cys157 of OLS as illustrated in
In order to identify different starter units that can perform the same three elongation steps using an extender unit such as malonyl-CoA, the last intermediate state that is still covalently attached to OLS, i.e., a triketide intermediate, 3, 5-dioxo decanoyl-CoA (after extension with two units of malonyl-CoA), was docked using GOLD (Groom et al.; see
The last malonyl-CoA unit was then superimposed in using the crystallized malonyl-CoA ligand complexed with a homologous protein, chalcone synthase (CHS2) from the legume Medicago sativa (PDB code: 1CML) (Ferrer et al., Nat. Struct. Biol., 1999, 6(8):775-784). The superimposed malonyl-CoA ligand (yellow ligand in
As mentioned above a library of 70 acyl-CoA starter units (Go et al.) and 12 different acyl-CoA extender units (Go et al., ACS Catalysis, 2015, 5(7):4033-4042) is available. Collectively, this equates to a total of 840 combinations of starter and extender units that can serve as substrates for type III polyketide synthases such as OLS. These are used as the substrate library to be docked into the OLS structure. The outputs of the docking results are ranked accordingly and compared with experimental results to check for accuracy of the prediction model. This experimental testing of substrate promiscuity of OLS will produce olivetolic acid analogues with a varied chain length or R-group that can then be used to produce cannabinoids with a varied R-group on C2 of the olivetolate-cannabinoid scaffold (see
Protein engineering is a long established field of engineering enzymes to specific desired characteristics. Yet, without a good selection method, the vast amount of sequence space requres a prediction model in selecting mutants to display product diversity.
As mentioned above, NphB mutants were designed with a high selectivity for producing CBGA without any side product. Different NphB mutants were designed such that this prenyltransferase accepts different substrates and thus produces a different desired cannabinoid product.
The last cyclization step in the cannabinoid biosynthetic pathway cyclizes the C10 chain previously transferred from GPP (see
An orthologue library of cannabinoid synthases are screened against CBGA-analogue producing strains to test for production of varied cannabinoid chemical structures that are subsequently tested for bioactivity.
All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.
From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the scope of the following claims. What is claimed is:
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2020/050584 | 10/12/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62914058 | Oct 2019 | US |
