title: The important ergot alkaloid intermediate chanoclavine-I produced in the yeast Saccharomyces cerevisiae by the combined action of EasC and EasE from Aspergillus japonicus.
abstract: BACKGROUND
  Ergot alkaloids are a group of highly bioactive molecules produced by a number of filamentous fungi. These compounds have been intensely studied for decades, mainly due to their deleterious effects in contaminated food and feeds, but also for their beneficial pharmaceutical and agricultural applications. Biosynthesis of ergot alkaloids goes via the common intermediate chanoclavine-I, and studies of the key enzymes, EasE and EasC, involved in chanoclavine-I formation, have relied on gene complementation in fungi, whereas further characterization has been hampered by difficulties of poor EasE protein expression. In order to facilitate the study of ergot alkaloids, and eventually move towards commercial production, the early steps of the biosynthetic pathway were reconstituted in the unicellular yeast Saccharomyces cerevisiae.
  
  
  RESULTS
  The genomic sequence from an ergot alkaloid producer, Aspergillus japonicus, was used to predict the protein encoding sequences of the early ergot alkaloid pathway genes. These were cloned and expressed in yeast, resulting in de novo production of the common intermediate chanoclavine-I. This allowed further characterization of EasE and EasC, and we were able to demonstrate how the N-terminal ER targeting signal of EasE is crucial for activity in yeast. A putative, peroxisomal targeting signal found in EasC was shown to be nonessential. Overexpression of host genes pdi1 or ero1, associated with disulphide bond formation and the ER protein folding machinery, was shown to increase chanoclavine-I production in yeast. This was also the case when overexpressing host fad1, known to be involved in co-factor generation.
  
  
  CONCLUSIONS
  A thorough understanding of the enzymatic steps involved in ergot alkaloid formation is essential for commercial production and exploitation of this potent compound class. We show here that EasE and EasC are both necessary and sufficient for the production of chanoclavine-I in yeast, and we provide important new information about the involvement of ER and protein folding for proper functional expression of EasE. Moreover, by reconstructing the chanoclavine-I biosynthetic pathway in yeast we demonstrate the advantage and potential of this host, not only as a convenient model system, but also as an alternative cell factory for ergot alkaloid production.
authors.forename: Curt A F
authors.initials: CA
authors.lastname: Nielsen
authors.forename: Christophe
authors.initials: C
authors.lastname: Folly
authors.forename: Anaëlle
authors.initials: A
authors.lastname: Hatsch
authors.forename: Andrea
authors.initials: A
authors.lastname: Molt
authors.forename: Hartwig
authors.initials: H
authors.lastname: Schröder
authors.forename: Sarah E
authors.initials: SE
authors.lastname: O'Connor
authors.forename: Michael
authors.initials: M
authors.lastname: Naesby
mesh_terms: D001230:Aspergillus; D053898:Biosynthetic Pathways; D004873:Ergolines / Q000737:chemistry / Q000378:metabolism*; D004876:Ergot Alkaloids / Q000096:biosynthesis* / Q000737:chemistry; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D005800:Genes, Fungal; D005818:Genetic Engineering; D016366:Open Reading Frames / Q000235:genetics; D020675:Peroxisomes / Q000378:metabolism; D021382:Protein Sorting Signals; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D004873:Ergolines; D004876:Ergot Alkaloids; D005656:Fungal Proteins; D021382:Protein Sorting Signals; C006959:chanoclavine; D014364:Tryptophan
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