Vindoline, biosynthesis

Salutaridinol 7-0-acetyltransferase catalyzes the conversion of the phenanthrene alkaloid salutaridinol to salutaridinol-7-Oacetate, the immediate precursor of thebaine along the morphine biosynthetic pathway in P. somniferum (Fig. 10.7).26 Acetyl CoA-dependent acetyltransferases have an important role in plant alkaloid metabolism. They are involved in the synthesis of monoterpenoid indole alkaloids in medicinal plant species such as Rauwolfia serpentina. In this plant, the enzyme vinorine synthase transfers an acetyl group from acetyl CoA to 16-epi-vellosimine to form vinorine. This acetyl transfer is accompanied by a concomitant skeletal rearrangement from the sarpagan- to the ajmalan-type (reviewed in2). An acetyl CoA-dependent acetyltransferase also participates in vindoline biosynthesis in Catharanthus roseus, the source of the chemotherapeutic dimeric indole alkaloid vinblastine (reviewed in2). Acetyl CoA deacetylvindoline 4-O-acetyltransferase catalyzes the last step in vindoline biosynthesis. A cDNA encoding acetyl CoA deacetylvindoline 4-0-acetyltransferase was recently successfully isolated.27... 

ST-PIERRE, B., LAFLAMME, P ALARCO, A.-M., DE LUCA, V., The terminal O-acetyltransferase involved in vindoline biosynthesis defines a new class of proteins responsible for coenzyme A-dependent acyl transfer, Plant J., 1998,14, 703-713. 

Lor most of this work, optimised in vitro plant cell suspension cultures were used, especially from R. serpentina and C. roseus, and in the latter case, differentiated tissue (seedling) was also successfully used for investigation of various aspects of vindoline biosynthesis [12, 13]. 

The translocation of pathway intermediates is also suggested by differential localization of TLA biosynthetic enzymes. In situ hybridization and immunolocalization studies have shown that CYP72A1, TDC, and STR are localized to the epidermis of immature leaves, stems, and flower buds.52,147 In contrast, D4H and DAT are associated with laticifers and idioblasts of shoot organs. Laticifers and idioblasts are distributed throughout the mesophyll in C. roseus leaves, and are often several cell layers away from the epidermis. Vindoline biosynthesis involves at least two distinct cell types and requires the intercellular translocation of a pathway intermediate (Fig.7.9B). The differential localization of the early and late steps of vindoline biosynthesis might partially explain why this alkaloid is not produced in dedifferentiated C. roseus cell cultures. 

Enzymes involved in vindoline biosynthesis have been localized to no fewer than five subcellular compartments in at least two distinct cell types (Fig.7.9B). The conversion of tryptophan to tryptamine by TDC occurs in the cytosol.151,152 Since... 

FAHN, W., GUNDLACH, H., DEUS-NEUMANN, B., STOCKIGT, J., Late enzymes of vindoline biosynthesis. Acetyl-CoA 17-0-deacetyIvindoline 17-0-acetyltransferase. Plant Cell Rep., 1985, 4, 333-336. 

DE CAROLIS, E., CHAN, F., BALSEVICH, J., DE LUCA, V., Isolation and characterization of a 2-oxoglutarate-dependent dioxygenase involved in the second-to-last step in vindoline biosynthesis. Plant Physiol., 1990,94,1323-1329. 

The association of cytochrome P450s with organelles other than the ER may have important implications for the biosynthesis of alkaloids. It may help to explain why biochemical localization studies have shown that certain reactions in a pathway occur within the chloroplast. In the case of Catharanthus alkaloids, the 3 rd to last step in vindoline biosynthesis involves a chloroplast thylakoid associated N-methyltransferase.22 The arguments for participation of chloroplasts in this reaction include the possibility that the previous step involving hydration of the 2,3 double bond might require a chloroplast based oxidation reaction (Fig 8.6). The conclusive identification of specific cytochrome P4S0 enzymes in chloroplasts suggests that this hypothesis should be tested. 

Fig. 8.6 Hypothetical model for the mobilization of 16-methoxytabersonine into the chloroplast in order to accommodate the 4th (hydration of 2,3 double bond) and 3rd (iV-methylation) to last steps in vindoline biosynthesis.

Extensive studies to quantitate the production of indole alkaloids in Catharanthus roseus hairy root cultures have revealed that they accumulate several compounds including ajmalicine, serpentine, catharanthine, tabersonine, horhammericine, and lochnericine.27, 28 The presence of tabersonine in hairy roots has raised speculations that this intermediate in vindoline biosynthesis, together with catharanthine, is transported from this potential site of biosynthesis through the vasculature to the stem and to the leaves where tabersonine is further elaborated into vindoline within laticifers and/or idioblasts.26 However, oxidized derivatives of tabersonine, such as horhammericine and lochnericine, are present at 5 to 15 times the levels of tabersonine in hairy roots,27 and presumably this prevents their transport and/or use for vindoline biosynthesis. In this context, it would be interesting to... 

DETHIER, M., DELUCA, V., Partial-purification of an N-methyltransferase involved in vindoline biosynthesis in Catharanthus roseus., Phytochemistry., 1993, 32, 673-678. 

Aerts, R.J. and De Luca, V. (1992) Phytochrome is involved in light-regulation of vindoline biosynthesis in Catharanthus. Plant Physiol., 100, 1029-32. 

St. Pierre B, Laflamme P, Alarco A, de Luca V. The terminal 119. O-acetyltransferase involved in vindoline biosynthesis defines a... 

Treatment of the seedlings with auxins enhanced the TDC activity the light-induction of DAT (see earlier discussion) was delayed 24 h through such a treatment (301). The finding that heterotrophic cell cultures of C. roseus contain vindoline 235) is in accordance with vindoline biosynthesis being found in the green tissues of the plant. 

In the plant, the enzymes of the vindoline pathway, DAT (236,247) and NMT (242), are only found in the aerial parts, and in particular the leaves, the site of vindoline biosynthesis. In C. roseus cell cultures these enzymes cannot be detected, either after elicitation or in photoautotrophic or hormone autotrophic cultures (242). However, two enzymes of the early steps of the vindoline pathway, TllH and 11-O-methyltransferase are also present in cell cultures although at lower levels than in the plant (241). In the plant, the highest TllH levels are found in young leaves, whereas it is absent in stems and old leaves. 

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