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The pharmacological effects of the ergot alkaloids as a group are complex and variable, with the net result of their actions depending on the effects at different receptors of the CNS. The pharmacological activities arise most probably from the structural similarity between D-lysergic acid-derived compounds and three important neurotransmitters; the structures of noradrenalin, dopamine and serotonin (5-hydroxytryptamine, 5-HT) can be mapped almost entirely onto the D-lysergic acid ring structure (Fig. 2). Many ergot alkaloids can probably interact with receptors for all three of these neurotransmitters (Berde and Stürmer, 1978), as either an agonist or antagonist, or even in a dual role as partial agonist and antagonist, depending on the substituents attached to the carboxyl group of D-lysergic acid (Stadler and Giger, 1984). This broad specificity can provoke undesired side effects and the approaches to improve natural ergot alkaloids as therapeutic agents involve narrowing the specificity of the compounds by chemical modification (Vendrell et al., 2007). Interestingly, the derivatives of D-isolysergic acid, the stereoisomer of D-lysergic acid, show little or no pharmacological activity, making a total chemical synthesis of ergot alkaloids challenging. In general, ergopeptines exert vasoconstrictive and sympatholytic–adrenolytic effects because of their affinity for adrenergic receptors (for a recent review, see Görnemann et al., 2008); however, the introduction of unnatural side-chains has drastic effects. Thus, the simple derivative dihydroergotamine can affect a1- and a2-adrenergic receptors and has a much more dominant adrenolytic effect with a concomitant reduction in the vasoconstrictive effect (Villalon et al., 1999; Willems et al., 1999). Dihydroergotamine is mainly used in the treatment of migraine (Tfelt-Hansen and Koehler, 2008). Dihydroergotoxin, a mixture of several ergopeptines, finds application as an antihypertensive agent and in the treatment of cerebral dysfunction in the elderly (de Groot et al., 1998; Wadworth and Crisp, 1992). Ergotoxines, including ergocryptine, have been shown to have an inhibitory effect on the release of the peptide hormone prolactin. Thus, 2-bromo-ergocryptine (bromocriptine) is also effective in cases of hyperprolactinaemia, a condition that can result in reproductive disorders, such as galactorrhoea, prolact independent mammary carcinoma, amenorrhoea, acromegaly or anovulation, and long-term complications, e.g. osteoporosis (Crosignani, 2006). Bromocriptine also has affinity to dopaminergic receptors, which became the basis for its use in the treatment of Parkinson’s disease (Thobois, 2006). In general, the broad activity spectrum of natural or semisynthetic ergot alkaloids renders them ‘dirty’ drugs, which are being increasingly substituted by synthetic derivatives with a more defined mode of action. Nevertheless, they still play a major role in the treatment of migraine and degenerative diseases of the CNS (Sinz, 2008). 2.2 Biosynthesis: the ergot alkaloid gene cluster Much of the knowledge about the biosynthesis of ergot alkaloids stems from feeding experiments with radiolabelled putative precursors or intermediates added to rye ears infected with C. purpurea or to fermentation cultures of C. purpurea, Claviceps fusiformis or Claviceps paspali (Keller and Tudzynski, 2002). The subsequent analysis of the biotransformation products established the biosynthetic building blocks of the ergoline ring system as tryptophan, the methyl group of methionine and an isoprene unit derived from mevalonic acid (Fig. 3) (for a recent review, see Schardl et al., 2006). The pathway leading to ergopeptines starts with the isoprenylation of tryptophan, yielding 4-dimethylallyltryptophan (DMAT). The enzyme catalysing this determinant step, dimethylallyl tryptophan synthase (DMATS), was the first to be characterized in detail (Gebler and Poulter, 1992). As might be expected for the determinant step, DMATS is subject to strict regulation: tryptophan serves as inducer, whereas elymoclavine or agroclavine causes feedback regulation of the enzyme (Cheng et al., 1980). Based on oligonucleotides derived from a partial amino acid sequence of the purified enzyme, the gene dmaW encoding DMATS was cloned, originally from a C. fusiformis strain (Tsai et al., 1995), and later from C. purpurea strain P1 (Tudzynski et al., 1999). A chromosome walking approach starting from dmaW led to the detection of a cluster of 14 genes, shown (or predicted) to encode ergot alkaloid biosynthetic enzymes (Fig. 4) (Haarmann et al., 2005; Lorenz et al., 2007; Tudzynski et al., 1999). Recently, in order to facilitate discussion of the genes and comparisons amongst ergot alkaloid-producing fungi, a systematic set of names for the genes of the ergot alkaloid pathway has been agreed upon by the groups involved in the analysis (Schardl et al., 2006). Claviceps purpurea alkaloid cluster genes that have not yet been functionally characterized are designated easA through easH (ergot alkaloid synthesis). Genes whose products have been biochemically characterized are named according to the enzyme activities of the encoded proteins. A list of the genes and their shown or predicted function is given in Table 1. In addition to dmaW, seven enzyme-encoding eas cluster genes have so far been functionally analysed by gene disruption and analysis of intermediates in C. purpurea P1. These include four non-ribosomal peptide synthetase (NRPS) genes, lpsA1/A2, lpsB and C. Biochemical evidence has shown that the final steps of ergopeptine synthesis in C. purpurea include a complex of two interacting NRPSs (a new finding in fungi): D-lysergyl peptidyl synthetase 2 (LPS2), catalysing the activation of lysergic acid, and LPS1, forming the tripeptide moiety (Fig. 3B; Riederer et al., 1996). Functional analysis has shown that lpsA1 and lpsA2 both encode LPS1 enzymes: LPS1-1 necessary for the synthesis of the major alkaloid of strain P1, ergotamine, and LPS1-2 for the synthesis of ergocryptine (Haarmann et al., 2008; Tudzynski et al., 1999). The gene lpsC probably encodes a monomodular NRPS enzyme that catalyses the formation of ergonovine (= ergometrine), an ergopeptine with a single amino acid sidechain (I. Ortel and U. Keller, FU Berlin, personal communication). Thus, this set of NRPS genes encodes a highly flexible natural combinatory system unique in eukaryotes: activated lysergic acid formed by LPS2 can be used as a recipient for the addition of several peptide moieties, explaining the high variability of the ergot peptide alkaloid spectrum in C. purpurea strains. Of the enzymes involved in the pathway from DMAT to lysergic acid, to date two genes have been identified by a knock-out approach: the gene product of cloA has been shown to catalyse the conversion of elymoclavine to paspalic acid (see Fig. 3) (Haarmann et al., 2006), and easE encodes the chanoclavine synthase (N. Lorenz and P. Tudzynski, unpublished data). The role of the gene product of easC, a putative catalase, is yet to be determined. Heterologous expression of easC in Pichia demonstrated catalase activity; a DeasC mutant produces no detectable amounts of alkaloids or intermediates, and the transcription of the other cluster genes is down-regulated, suggesting a regulatory function (T. Haarmann, N. Lorenz, S. Giesbert and P. Tudzynski, unpublished data). 2.3 Biotechnology The industrial production of ergot alkaloids began with the patent of A. Stoll on the production of ergotamine tartrate, which was used by Sandoz as early as 1921; Sandoz dominated the world market in alkaloid production up to the 1950s, when competitors such as Boehringer Ingelheim, Galena, Gedeon Richter, Eli Lilley and Farmitalia appeared (see review by Cvak, 1999). Claviceps purpurea, C. fusiformis and C. paspali were generally used as production strains. These species differ considerably with respect to their potential to synthesize specific alkaloids: only C. purpurea produces peptide alkaloids, whereas single lysergic acid derivatives are produced by C. paspali, and C. fusiformis is used to produce clavine alkaloids. Originally, the field production of alkaloids on rye or triticale was the major production method, but the submersed production with specially designed strains soon prevailed (Keller and Tudzynski, 2002; Tudzynski et al., 2001). Today, the production of single clavine alkaloids or paspalic/lysergic acid is of major importance as a basis for semi-synthetic drug development; the annual production of all ergopeptines is estimated to reach 5000–8000 kg, whereas about 10 000–15 000 kg of lysergic acid is (legally) produced annually (Schiff, 2006).