Enzymes in Ergot alkaloid biosynthesis

Experiments have been carried out with elymoclavine (73) in whole cells and protoplasts of Claviceps strain SD 58 levels of dimethylallyltryptophan synthetase, the first enzyme in ergot alkaloid biosynthesis, were measured.64 The results that were obtained provide strong evidence that there is end-product regulation of the synthesis of alkaloids in vivo and that it involves feedback inhibition end-product repression of the synthesis of enzymes appears to be of lesser importance. 

Shibuya, M., Chou, H.-M., Fountoulakis, M., Hassam, S., Kim, S.-U., Kobayashi, K., Otsuka, H., Rogalska, E., Cassady, J.M. and Floss, H.G. (1990) Stereochemistry of the isoprenylation of tryptophan catalysed by 4-( Y, Y-dimethylallyl)tryptophan synthase from Claviceps, the first pathway-specific enzyme in ergot alkaloid biosynthesis. /. Am. Chem. Soc., 112, 297-304. 

Cheng JZ, Coyle CM, Panaccione DG, O Connor SE (2010) A role for old yellow enzyme in ergot alkaloid biosynthesis. J Am Chem Soc 132 1776-1777... 

Ergot Alkaloids.—The enzyme which catalyses the first step in ergot alkaloid biosynthesis, namely the conversion of tryptophan into dimethylallyltryptophan (126),110 has been isolated from a Claviceps species and characterized.111 The biosynthesis of clavicipitic acid (127) may be a major alternative to the synthesis of other ergot metabolites, and further results in a study112 of an enzyme from C. purpurea which catalyses the formation of clavicipitic acid (127) from (126) have been published.113... 

Figure 1 Key intermediate and enzymes from the first committed step in ergot alkaloid biosynthesis through the synthesis of lysergic acid. Simple amides of lysergic acid and ergopeptines are covered in Figs 2 and 3, respectively. Abbreviations DMAPP = dimethylallyl pyrophosphate DMAT = dimethylallyl tryptophan AdoMet = S-adenosyl-methionine.

GENES ENCODING ENZYMES INVOLVED IN ERGOT ALKALOID BIOSYNTHESIS... 

Dimethylallyltryptophan (139) has been identified as the first intermediate after tryptophan in ergot alkaloid biosynthesis.In experiments with a Claviceps species, clavicipitic acid (140) was identified as a major product formed from (139).(The enzyme catalysing this transformation was identified in both the supernatant and microsonal fractions oxygen is necessary for the reaction but cytochrome P-450 does not appear to be involved.) But radioactive clavicipitic acid was found to be a much less efficient precursor than (139) for elymoclavine and thus is in all probability not an intermediate in ergot alkaloid biosynthesis. 

Lee, S.L., Floss, H.G. and Heinstein, P. (1976) Purification and properties of dimethylallylpyrophosphate tryptopharm dimethylallyl transferase, the first enzyme of ergot alkaloid biosynthesis in Claviceps. sp. SD 58. Arch Biochem Biophys., 77, 84-94. 

Ergot alkaloid biosynthesis and lipid metabolism have some common regulatory points. Hydroxymethylglutaryl-coenzyme-A reductase is the key regulatory enzyme of isoprenyl unit production. The activity pattern of this enzyme in Claviceps (Kfen et al., 1986) reveals that the mevalonate distribution is shared at the beginning of the fermentation by sterol and alkaloid biosynthesis and later it is used solely for alkaloid building. 

Alkaloids of this group are susceptible to oxidative biotransformations by many microorganisms resulting in N-demethylation, C-hydroxylation, or ring-closure reactions (11). Many of the observed biotransformations parallel or are closely related to processes thought to occur in the normal biosynthesis of the ergot alkaloids and may indeed involve the same or similar enzyme systems to those responsible for the normal production of the alkaloids themselves (11, 64, 65). 

Scheme 8. Biosynthesis of ergot alkaloids. Selective inhibition of DMAT-synthase in the biosynthesis pathwayby 5-fluorotryptophan blocks synthesis of alkaloids de novo but does not influence other biochemical processes in the cells, e. g., transfructosylating enzymes [27]...

Biosynthesis of ergot alkaloids has received wide attention and extensive studies have been made (Riederer et al., 1996 Walzel et al., 1997). This has led to the identification of several enzymes involved in the biogenetic pathway... 

In the course of their studies on the biosynthesis of ergot alkaloids. Robbers and Floss isolated clavidpitic acid, a new indolic amino acid [89]. Based on the X-ray crystal data of the major isomer and the assumption that the stereocenter at C-5 retains its stereochemistry from L-tryptophan, the structure shown in Scheme 59 was assigned [90]. By performing feeding experiments on Claviceps sp. SD 58 with clavicipitic acid (biosynthetically labeled), the laboratories of Floss [90] and Anderson [91] independently determined that clavicipitic acid is not a precursor to elymoclavine. Instead, Floss argues that it arises from ... a derailment of the metabolism leading to the tetracyclic ergolines between the first and second pathway-specific steps, the isoprenylation of tryptophan and the N-methylation of 4-(y,y-dimethylallyl)-tryptophan (DMAT). Anderson and co-workers isolated an enzyme, DMAT oxidase, from Claviceps sp. which catalyzes the formation of clavicipitic acid from DMAT [92]. The enzyme, which requires... 

Four enzymes which are involved in the biosynthesis of the ergot alkaloids have now been isolated from Claviceps. The other three are 4-dimethylallyltryptophan synthase , chanoclavine-I cyclase , and agroclavine hydroxylase . ... 

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