Biosynthesis strictosidine

The in vivo transformation of [6-14C]strictosidine (19) to gelsemine in Gelsemium sempervirens was claimed with an incorporation of 0.47% (33). This provides another experimental support to the proposal that strictosidine appears to be the original precursor in the biosynthesis of monoterpenoid indole alkaloids, although the detailed pathway of this biosynthetic process still remains obscure. 

Since the last major review of the biosynthesis of the monoterpenoid indole alkaloids (97), there have been several full and partial 98-104) reviews of various aspects of the work that has been conducted since 1974. Two major developments have dominated the field in this period, namely, the demonstrations that (i) strictosidine (33) is the universal precursor of the monoterpenoid indole alkaloids and (ii) selected cell-free systems of C. roseus have the ability to produce the full range of alkaloid structure types, including the bisindoles. This section traces some aspects of these developments, paying particular attention to work been carried out with C. roseus, and omitting work, important though it may be, on other monoterpenoid indole alkaloid-producing plants, e.g., Rauwolfia, Campto-theca, and Cinchona. 

Although ajmalicine (39) is not on the pathway to the bisindole alkaloids, it is a compound of substantial commercial interest, and several of the intermediates in its formation are probable intermediates in the extended biosynthetic pathway. This work is therefore reviewed for the purpose of completeness of studies on C. roseus. Considerable progress has been made on the biosynthesis of ajmalicine (39), and the studies on the formation of strictosidine (33) and cathenamine (76) have already been described. One of the preparations described by Scott and Lee was a supernatant from a suspension of young seedlings of C. roseus which af-... 

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. 

Gene transfer from the angiosperm Catharanthus roseus, and over-expression in the bacterium Escherichia coli, yielded the synthase for strictosidine, a known alkaloid of the tryptophan-secologanin class (Scott 1992). A similar strategy has clarifted the biosynthesis of hydrogenobyrinic acid, an advanced precursor of vitamin B,2 (Scott 1994). 

As far as biosynthesis is concerned, it is clear that lyaloside (23) and pauridianthoside (26) readily derive from strictosidine (17). These three molecules display identical stereochemistry at the three chiral centers, namely, a,a,(3 for the hydrogen atoms at the 15, 20, 21 positions, respectively. They are closely related to a number of glucoalkaloids identified in Pertusadina euryncha (= Adina rubescens), e.g., rubenine (31) and desoxycordifoline (34, R = H) (49), and in Adina cordifolia, e.g., cordifoline (34, R = OH) (50). Palinine (35),... 

In the course of this chapter devoted to the alkaloids of Pauridiantha, their biosynthesis has been mentioned and some chemotaxonomic correlations have been proposed. As all glucoalkaloids described here derive from strictosidine, a more systematic analysis of its metabolic evolution in plants seems of interest. 

Terpenoid Indole Alkaloids.—Important recent work has defined strictosidine (97) as a key intermediate in the biosynthesis of terpenoid indole alkaloids with both 3a- and 3/3-configurations. Some of this work, published earlier in preliminary form (cf. Vol. 9, p. 18), is now available in a full paper.26 In addition to those alkaloids examined earlier, strychnine, gelsemine, vincadifformine, isoreserpiline, aricine, isoreserpinine, and ajmaline have been shown to derive from strictosidine (data are also included for ajmalicine, for catharanthine, and for vindoline which had been reported earlier). 

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...

GEERLINGS, A., MARTINEZ-LOZANO IBANEZ, M., MEMELINK, J., VAN DER HEIJDEN, R., VERPOORT, R., Molecular cloning and analysis of strictosidine P-D-glucosidase, an enzyme in terpenoid indole alkaloid biosynthesis in Catharanthus roseus. J. Biol. Chem., 2000,275,3051-3056. 

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. 

The enzyme STR1 that was first characterized in Catharanthus roseus cell suspension cultures produces the central indole alkaloid intermediate H-3-a-(S)-strictosidine from tryptamine and secologanin (Fig. 8.9). It is well known that strictosidine represents the central intermediate precursor for several thousand indole alkaloids found in Nature. STR1 was the first gene to be cloned from R serpentina that involved a committed step in alkaloid biosynthesis.31 This was soon followed by the identification and isolation of an STR clone from Catharanthus roseus32 whose sequence was 80 % identical to the same gene from R serpentina.31... 

The versatility of strictosidine as a central intermediate for the biosynthesis of a variety of alkaloids is based on the highly reactive dialdehyde produced by the action of strictosidine p-D-glucosidase. This reactive intermediate is converted by uncharacterized enzymes into the major corynanthe, iboga, and aspidosperma skeletons that are elaborated into die several hundred alkaloids found in Catharanthns roseus. Since the biosynthesis of strictosidine appears to occur within plant vacuoles, there has been much speculation, but little is known, about the factors that regulate the accumulation of strictosidine within the vacuole, or which trigger its mobilization for further elaboration. It is well known that glycosides of different natural product classes are located within plant vacuoles. 

Another all-carbon Diels-Alder reaction is proposed for the biosynthesis of the indole alkaloids tabersonine 1-6 and catharanthine 1-7 of the Aspidosperma and Iboga family [28-31]. The compounds are formed via strictosidine 1-3, the first nitrogen-containing precursor of the monoterpenoid indole alkaloids, and stemmadenine 1-4, which is cleaved to give the proposed intermediate dehy-drosecodine 1-5 with an acrylate and a 1,3-butadiene moiety (Scheme 1-1). 

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... 

In their studies on the biosynthesis of terpenoid indole alkaloids, De Silva and co-workers have carried out a screening of some indole alkaloid producing plants of Sri Lanka for the occurrence of the first nitrogenous monoterpenoid precursor (70,71). In this survey, Rauvolfia serpentina, Strychnos nux-vomica, Cinchona ledgeriana, and a number of Mitragyna and Vinca species were tested for the presence of vincoside and 5a-carboxyvincoside. Although these two proposed bio-intermediates (at the time) were not detected, macroisolation techniques revealed the occurrence of 5a-carboxystrictosidine (78), an isomer of 5a-carboxyvincoside, in all plants tested, and strictosidine (79), an isomer of vincoside, only in... 

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