Biology subjects

Gelinas, S.-E.

Publications and source records attributed to Gelinas, S.-E..

3 recordsLinked to original sources

bioRxiv2025

Branch-Enabling N-Methyltransferase in Golgi Reconciles Divergent Models of Galanthamine Biosynthesis

Galanthamine, a therapeutic Amaryllidaceae alkaloid produced exclusively by species within the Amaryllidoideae subfamily, is a key treatment for early-stage symptoms of Alzheimers disease. Elucidating its biosynthetic pathway is essential for strategies aimed at enhancing production through metabolic engineering. Galantamine derives from the metabolic precursor 4'-O-methylnorbelladine, which undergoes cytochrome P450-mediated para-ortho C-C phenol coupling to yield nornarwedine. Two competing terminal routes have been proposed: (i) reduction of nornarwedine to norgalanthamine, followed by N-methylation, or (ii) N-methylation of nornarwedine to narwedine prior to reduction. Here, we identify three N-methyltransferase (NMT) candidates from Leucojum aestivum: LaNMT, related to coclaurine NMTs, and two {gamma}-tocopherol methyltransferases (TMT) homologs, LaTMT1 and LaTMT2. Subcellular localization studies revealed distinct compartmentalization, with LaNMT targeted to the ER-cytosol, LaTMT1 to plastids, and LaTMT2 to the Golgi apparatus. In vitro enzyme assays demonstrated that LaTMT2 methylates both nornarwedine and norgalanthamine, with a kinetic preference for nornarwedine. Agroinfiltration for transient expression in Nicotiana benthamiana further confirmed LaTMT2 as a catalytically efficient and substrate-promiscuous enzyme that supports both terminal routes. These findings identify LaTMT2 as a key branch-enabling N-methyltransferase that reconcile long-standing models of galanthamine biosynthesis and provides a strategic target for metabolic engineering strategies to enhance galanthamine production. Significant statementThis study identifies LaTMT2, a Golgi-localized {gamma}-tocopherol methyltransferase homolog, as a branch-enabling N-methyltransferase that resolves competing models of galanthamine biosynthesis. By revealing an unanticipated Golgi-associated step in Amaryllidaceae alkaloid metabolism, it redefines the subcellular organization of specialized metabolic pathways and provides a strategic enzymatic target for metabolic engineering of high-value therapeutic alkaloids.

plant biology↗

bioRxiv2025

Insights into cannabinoid biosynthesis in Chlamydomonas reinhardtii : successes with NphB and limitations of CBDAS expression

The growing legalization of Cannabis has increased demand for cannabinoids (CBs). Currently, pharmaceutically relevant CBs are primarily extracted from Cannabis, a process that presents challenges related to yield variability and purity. To overcome these limitations, microbial platforms are being explored for the sustainable production of specific CBs. Compared to conventional microbial hosts, the photosynthetic microalga Chlamydomonas reinhardtii offers plant-like post-translational modifications, low-cost cultivation, CO2 fixation, and low endotoxin contamination, making it a potential chassis for CB biosynthesis. Here, we expressed a codon-optimized, soluble aromatic prenyltransferase (NphBG286S/Y288A) from Streptomyces and Cannabis sativa cannabidiolic acid synthase (CBDAS) in the nuclear genome of C. reinhardtii; transformants were screened for integration, gene expression, protein accumulation, enzymatic activity, and CB production. Our results provide evidence of functional NphB expression in C. reinhardtii, with in vitro CBGA production reaching up to 633 {+/-} 58 {micro}g/L. Although CBDAS transcripts were detected under multiple construct designs, neither protein nor CBDA was accumulated, suggesting limitations in expression, localization, or post-translational processing in C. reinhardtii. Our study provides the first demonstration of in vitro CBGA biosynthesis in the photosynthetic model microalga C. reinhardtii, highlighting its potential as a future platform for CB production. It also highlights key challenges in nuclear expression of plant-derived enzymes, such as CBDAS, emphasizing that improved regulatory control, subcellular targeting, and mRNA processing will be required to achieve full pathway reconstruction in C. reinhardtii. HighlightsO_LIFirst report of active NphB expression in Chlamydomonas reinhardtii C_LIO_LINphB exhibits measurable in vitro activity, producing cannabigerolic acid in algal extracts C_LIO_LIEnzyme localization, construct design, and substrate availability critically influence functionality. C_LI

bioengineering↗

bioRxiv2022

Characterization of norbelladine synthase and noroxomaritidine/norcraugsodine reductase reveals a novel catalytic route for the biosynthesis of Amaryllidaceae alkaloids including the Alzheimer's drug galanthamine

Amaryllidaceae alkaloids (AAs) are a large group of pharmacological plant-specialized metabolites. Norbelladine is the entry compound in AAs biosynthesis. Two enzymes are capable of catalyzing this reaction in-vitro, both with low-yield; 1) norbelladine synthase (NBS) condenses tyramine and 3,4-dihydroxybenzaldehyde, while 2) noroxomaritidine/norcraugsodine reductase (NR), catalyzes a reduction reaction. To clarify the mechanisms involved in this controversial step, both NBS and NR were characterized from Narcissus papyraceus and Leucojum aestivum. Assays with each enzyme suggested that NBS and NR function together for norbelladine formation. Using molecular-homology modeling and docking studies, we predicted models for the binding of substrates to NBS and NR. Moreover, NBS and NR physically interact, localize to the cell cytoplasm and nucleus and are expressed at high levels in bulbs. Our study establishes that both NBS and NR participate in the biosynthesis of norbelladine, catalyzing the first key steps involved in the biosynthesis of the Alzheimers drug galanthamine.

biochemistry↗