Strictosidine synthase biosynthesis

Bracher, D. and Kutchan, T. M. 1992. Strictosidine synthase from Rauvolfia serpentina Analysis of a gene involved in indole alkaloid biosynthesis. Archives of Biochemistry and Biophysics, 294 717-723. 

Fig. 6 In vivo reprogramming of alkaloid biosynthesis in hairy roots of C. roseus by introduction of a mutant cDNA of the key enzyme strictosidine synthase (STR) with broader, unnatural substrate specificity leading to diversification of alkaloid content in roots following long-term feeding with 5-substituted tryptamines (X = Cl, Br, Me) [78]...

Fig. 3. Biosynthesis of TIAs in C. roseus. Solid arrows indicate single enzymatic conversions, whereas dashed arrows indicate multiple enzymatic conversions. AS Anthranilate synthase, DXS D-l-deoxyxylulose 5-phosphate synthase G10H geraniol 10-hydroxylase CPR cytochrome P450 reductase TDC tryptophan decarboxylase STR strictosidine synthase SGD strictosidine /1-D-glucosidase D4H desacetoxyvindoline 4-hydroxylase DAT acetyl-CoA 4-O-deacetylvindoline 4-O-acetyl transferase. Genes regulated by ORCA3 are underlined. Reprinted with permission from [91]. Copyright (2000) American Association for the Advancement of Science...

Fig. 8.1 Sequence of reactions and pathways involved in the biosynthesis of indole alkaloids in Catharanthus roseus. The dotted lines indicate multiple and/or uncharacterized enzyme steps. Tryptophan decarboxylase (TDC), Geraniol Hydroxylase (GH), Deoxyloganin synthase (DS), Secologanin Synthase (SLS) Strictosidine synthase (STR1), Strictosidine glucosidase (SG), Tabersonine-16-hydroxylase (T16H), Tabersonine 6,7-eposidase (T6,7E), Desacetoxyvindoline-4-hydroxylase (D4H), Deacetyl-vindoline-4-O-acetyltransferase (DAT) and Minovincinine-19-O-acetyltransferase (MAT) represent some of the enzyme steps that have been characterized.

SLS, CYP72A1) and strictosidine (strictosidine synthase, STR1) biosynthesis. 

Figure 2.12 A hypothetical view of compartmentation of indole alkaloid biosynthesis in Catharanthus roseus. Enzymes located with dashed arrows are hypothetical and circles indicate membrane associated enzymes (after Meijer et at, 1 993b). Cl OH, geraniol-1 0-hydroxylase NMT, 5-adenosyl-L-methionine 11 -methoxy 2,16-dihydro-16-hydroxytabersonine N-methyltransferase DAT, acetylcoenzyme A deacetylvindoline 1 7-0-acetyltransferase OHT, 2-oxyglutarate-dependent dioxygenase SSpC, strictosidine-((3)-glucosidase SSS, strictosidine synthase.

Keywords chemotaxonomy patchy distribution biosynthesis genes horizontal gene transfer endophytes evolution tryptophan decarboxylase tyrosine decarboxylase phenylalanine ammonia-lyase chalcone synthase strictosidine synthase berberine bridge enzyme codeine reductase... 

As in morphine biosynthesis, the knowledge of the enzyme sequences allows a more detailed understanding of the localization of the enzymes (104). Strictosidine synthase (Fig. 2b) seems to be localized to the vacuole (105), and strictosidine glu-cosidase is believed to be associated with the membrane of the endoplasmic reticulum (73, 106). Tabersonine-16-hydroxylase is associated with the endoplasmic reticulum membrane (98) N-methyl transferase activity is believed to be associated... 

Fig. (4). Early steps of the biosynthesis of terpenoid indole alkaloids in Catharanthus roseus. Triple arrowheads indicate multiple steps. G10H geraniol 16-hydroxylase TDC tryptophan decarboxylase STR strictosidine synthase.

The stereospecific condensation of tiyptamine and secologanin under the action of strictosidine synthase (STR), Fig. (4), is the first committed step in TIAs biosynthesis, and it yields the ghicoalkaloid 3-a(S)-strictosidine, which is the central biogenetic precursor of all TIAs [74-11]. 

Based on knowledge of a biosynthetic pathway one can select certain steps which could be of interest for bioconversion of (a) readily available precursor(s). This could, for example, be stereospecific reactions, like the reduction of quinidinone in quinine or quinidine and the epoxidation of atropine to scopolamine. For the bioconversion one can consider using plant cells [e.g., the production of L-dopa from tyrosine by immobilized cells of Mucuna pruriens (10)] or isolated enzymes from the plant itself. An interesting example of the latter is the (5)-tetrahydroprotoberberine oxidase (STOX) enzyme, which oxidizes (5)-reticuline but not its stereoisomer (11). This feature can be used in the production of (i )-reticuline from a racemic mixture (see below). Immobilized strictosidine synthase has been successfully used to couple secologanin and tryptamine. The gene for this enzyme has been isolated from Rauvolfia (6) and cloned in Escherichia coli, in which it is expressed, resulting in the biosynthesis of active enzyme (7). The cultured bacteria produced 20 times more enzyme... 

A key step in indole alkaloid biosynthesis is the formation of strictosidine from tryptamine and the aldehyde secologanin [357, 358]. This reactimi is catalyzed by the enzyme strictosidine synthase. The crystal structure of the enzyme has been determined and the binding site identified [359]. Site-directed mutagenesis has been used to identify both the active site amino acids and to modify the substrate specificity of the enzyme [360]. The enzymatic mechanism has been compared with the H -catalyzed reaction in solution and they appear to be similar, based on... 

Biosynthesis The biosynthesis of these alkaloids begins with the key reaction, the condensation of tryptamine with secologanin to give strictosidine catalyzed by the enzyme strictosidine synthase. The biosynthesis was elucidated mainly by the use of plant cell suspension cultures. Cell cultures of Catharanthus and Rauvolfia species have been the subject of intense phytochemical studies. 

Figure Simplified scheme for the biosynthesis of the antiar- > rhythmic agent ajmaline. Only the key steps are shown in the scheme. The cofactors given on the left side participate in individual enzymatic reactions. The following enzymes were identified in the 15-step sequence leading to the final product ajmaline 1 strictosidine synthase 2 strictosidine glucosidase ...

Stockigt, J., et al., 3D-Structure and function of strictosidine synthase—the key enzyme of monoterpenoid indole alkaloid biosynthesis. Plant Physiol Biochem., 2008. 46(3) p. 340-55. 

Fig. 8.5 Compartmentation of alkaloid biosynthesis in Cathamnthus roseus. AS anthianilate synthase, CR NADPH cathenamine reductase, DAT deacetylvindoline 17-O-acetyltransferase, ER endoplasmic reticulum, GlOH geraniol 10-hydroxylase, GAP glyceraldehyde-3-phosphate, NMT S-adenosyl-L-methionine methoxy-2, 16-dihydro-16-hydioxylagersonine-lV-methyltransferase, OHT desacetoxyvindoline-4-hydroxylase, SGD strictosidine -glucosidase, STR strictosidine synthase TDC tryptophan decarboxylase, THAS NADPH tetrahydroalstonine reductase (Adopted from Ref. [10])... 

Fig. 8.7 Biosynthetic pathway for monoteipenoid indole alkaloid (MIA) biosynthesis in plants. TDC tryptophan decarboxylase, STR strictosidine synthase, SGD strictosidine -o-glucosidase, T16H tabersonine 16-hydroxylase, D4H desacetoxyvindolme 4-hydroxylase, DAT deacetylvindoline 4-O-acetyltransferase (Adopted from Ref. [3])...

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