Engineering the biosynthesis of cannabis compounds
Phytochemicals include all of the wondrous substances found in plants, many of which contain powerful medicinal properties. Cannabinoids and terpenes from the cannabis plant have demonstrated a wide range of properties that can be effective in treating pain, anxiety, epilepsy, bacterial infections, and inflammation, among other conditions.1 However, similar compounds are also found in sources outside of cannabis.
Terpenes reside in a variety of other plants, one being linalool, which gives lavender its scent and anxiolytic properties.1 Echinacea also contains chemicals that interact with the cannabinoid 2 receptor, therefore potentially exerting some of its effects via the endocannabinoid system.2 But, can other plants or organisms produce the same cannabinoids as cannabis?
Just a few months ago, Luo et al. (2019), with colleagues at the University of California-Berkeley, published a report in the prestigious journal Nature in which they achieved just this—by producing cannabinoids in Saccharomyces cerevisiae, more commonly known as “baker’s yeast”.3
To accomplish this very formidable task, they first attempted to produce olivetolic acid, which plays a key role in the cannabinoid biosynthesis pathway, from galactose, a simple sugar. This required genetically altering the yeast strain by inserting two expression cassettes. Once they achieved success with this method, they were able to boost the production of olivetolic acid by feeding hexanoic acid to the modified strain.3
Following olivetolic acid production, the group went on to develop a form of the yeast strain containing an upregulated mevalonate pathway to create geranyl pyrophosphate (GPP). Cannabigerolic acid (CBGA) creates Δ9-tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA), which in turn produce several other cannabinoids. However, olivetolic acid cannot create CBGA without help from GPP via the enzyme geranylpyrophosphate:olivetolate geranyltransferase (GOT).3
The next step in this process involved identifying enzymes with GOT activity in yeast. Following additional modifications, three enzymes were used to generate a strain that produced CBGA from hexanoic acid. Finally, integration of the hexanoyl-CoA pathway ultimately led to CBGA production from galactose. This non-cannabis-derived CBGA then produced THCA (2.3 mg l−1), CBDA (4.2 μg l−1), Δ9-tetrahydrocannabivarinic acid (1.2 mg l−1), and cannabidivarinic acid (6.0 μg l−1).3
Additional work resulted in the creation of yeast cannabinoid analogues. These could potentially provide additional medicinal benefit through chemical modifications with further study.3
The results from these experiments represent a continuation of cannabis research breakthroughs from this lab, building upon previous evaluations in E. coli and successful production in yeast.4 The legal status of cannabis at the federal level has held back cannabis science and restricted access to these healing compounds. As the demand for cannabis extracts grows, so does the need to produce large quantities of cannabinoids, which is not currently possible due to the limitations of exogenous cannabinoid biosynthesis.
Creating cannabinoids from a non-cannabis source like yeast may provide an alternative– although it may be too soon to tell if this particular method will be able to scale-up production to exceed levels that can be extracted from the plant alone.
“It was an interesting scientific challenge,” said the study’s corresponding author, Jay Keasling, PhD, Professor of Chemical and Biomolecular Engineering and Bioengineering.
“But when you read about cases of patients who have seizures and are helped by CBD, especially children, you realize there is some value in these molecules, and that producing cannabinoids in yeast could really be great.”
Biochemical advancements hold potential in radically changing the way cannabinoids are produced, tested, and optimized for medical use. This study provides just one example of how cannabis scientists are using technology to create cannabinoids.
References
- Russo, E.B., “Taming THC: Potential Cannabis Synergy and Phytocannabinoid-terpenoid Entourage Effects.” Br J Pharmacol, vol.163, no.7, 2011, pp.1344-1364. (impact factor: 6.81; cited by: 596)
- Gertsch, J., et al., “Phytocannabinoids Beyond The Cannabis Plant – Do They Exist?” Br J Pharmacol. vol.160, no.3, 2010, pp. 523-529. (impact factor: 6.81; cited by: 121)
- Luo, X., et al., “Complete Biosynthesis of Cannabinoids And Their Unnatural Analogues in Yeast.” Nature. vol.567, no.7746, 2019, pp. 123-126. (impact factor: 41.577; cited by: 7)
- Zirpel, B., et al., “Production of Δ9-tetrahydrocannabinolic Acid from Cannabigerolic Acid by Whole Cells of Pichia (Komagataella) pastoris Expressing Δ9-tetrahydrocannabinolic Acid Synthase from Cannabis sativa L.” Biotechnology Letters, vol.37, no.9, 2015, pp. 1869-1875. (impact factor: 1.155; cited by: 23)
