Ergot alkaloids biosynthesis in Claviceps

Molecular Aspects of Host-Pathogen Interactions and Ergot Alkaloid Biosynthesis in Claviceps Paul Tudzynski and Klaus B. Tenberge... 

Matuschek M, Wallwey C, Xie X, Li S-M (2011) New insights into ergot alkaloid biosynthesis in Claviceps purpurea an agroclavine synthase EasG catalyses, via a non-enzymatic... 

The combination of classical and molecular genetic techniques opens interesting new perspectives of the analysis of ergot alkaloid biosynthesis in Claviceps and for the development of strain improvement programs. The available molecular techniques should allow in the near future the cloning of important genes of the... 

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. 

Kfen, V., Pazoutova, S., Rezanka, T., Viden, I., Amler, E. and Sajdl, P. (1990a) Regulation of lipid and ergot alkaloid biosynthesis in Claviceps purpurea by chlorophenoxy acids. Biochem. Physiol. Pflanzen, 186, 99-108. 

Milicic, S., Kremser, M., Gaberc-Porekar, V., Didek-Brumec, M. and Socic, H. (1987) Correlation between growth and ergot alkaloid biosynthesis in Claviceps purpurea batch fermentation. Appl. Microbiol. BiotechnoL, 27,117-120. 

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. 

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... 

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. 

Lorenz N, Wilson EV, Machado C, Schardl CL, Tudzynski P (2007) Comparison of ergot alkaloid biosynthesis gene clusters in Claviceps species indicates loss of late pathway steps in evolution of C.fusiformis. Appl Environ Microbiol 73 7185-7191... 

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. 

Tryptophan is a precursor of ergot alkaloids in Claviceps and in some cases plays also the role of an inducer and derepressor (Bu Lock and Barr, 1968 Vining, 1970 Robbers et al., 1972). Isotopically labelled tryptophan shown a high level of incorporation into ergot alkaloids (41%) in the strain of P. sizovae indicating that it is also here a direct precursor Kozlovsky et al. (1985). In Claviceps not only L- but also D-tryptophan are utilised for the ergot alkaloid biosynthesis (Robbers et al., 1972 Floss, 1976). The effect of both L- and D-tryptophan and also of their analogue, D,L-6-methyltryptophan on the alkaloid... 

A fascinating problem in the biosynthesis of ergot alkaloids is the mechanism by which dimethylallyltryptophan (102) is transformed through chanoclavine-I (103) to agroclavine (104) and elymoclavine (106), a reaction sequence which involves two cis-trans isomerizations in the side-chain double bond. Further evidence on the course of biosynthesis comes from feeding dimethylallyltryptophan labelled as shown in (102), to Claviceps penniseti. The alkaloids (103), (104), and (106) were isolated and the sites of labelling were determined to be as shown in Scheme 7. Thus the first double bond isomerization occurs between (102) and (103) and the second between (103) and (104). 

Ergot Alkaloids.—In connection with the biosynthesis of the ergot alkaloids it is of interest to note that 7V-methyl-4-dimethylallyltryptophan (49) has been isolated from cultures of Claviceps fusiformis grown anaerobically the presence of (49) could not be detected in cultures grown under normal aerobic conditions. An early stage in the biosynthesis of the alkaloids is the introduction of the allylic hydroxy-group, e.g. (50)- (51) whether the -methylation precedes or follows hydroxyla-tion is not known, but it seems certain that iV-methylation occurs before the cyclization-decarboxylation stage that results in formation of the tricyclic chano-clavines. 

Many of the intermediates and several of the enzymatic steps involved in the biosynthesis of ergot alkaloids have been studied in Claviceps species (e.g., Floss, 1976 Waller and Dermer, 1981 Kozikowski et al., 1988 Shibuya et al., 1990) and are outlined in Figs. 1-3. However, much about the pathway remains to be investigated. A similar pathway is expected in Neotyphodium, Epichloe, and Balansia spp. given their phylogenetic relationship to Claviceps (Glenn et al., 1996 Craven et al., 2001) and the presence of similar DNA sequences for two of the genes in the pathway (described below). 

Keller U. Biosynthesis of ergot alkaloids. In Kren V, Cvak L, eds. Ergot—The Genus Claviceps. London Harwood 1999, pp 95-163. 

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