Novel apocarotenoid intermediates in Neurospora crassa mutants imply a new biosynthetic reaction sequence leading to neurosporaxanthin formation

Fungal Genet Biol. 2008 Nov;45(11):1497-505. doi: 10.1016/j.fgb.2008.09.001. Epub 2008 Sep 10.


Neurosporaxanthin, beta-apo-4'-carotenoic acid (C35), represents the end-product of the carotenoid pathway in Neurospora crassa. It is supposed to be synthesized in three steps catalyzed by sequential AL-2, CAO-2 and YLO-1 activities: (i) cyclization of 3,4-didehydrolycopene (C40); (ii) cleavage of torulene into beta-apo-4'-carotenal (C35); and finally (iii) oxidation of beta-apo-4'-carotenal. However, analyses of the ylo-1 mutant revealed the accumulation of intermediates other than beta-apo-4'-carotenal. Here, we generated a 3,4-didehydrolycopene accumulating Escherichia coli strain and showed that CAO-2 cleaves this acyclic carotene in vivo and in vitro yielding apo-4'-lycopenal. The apocarotenoids accumulated in the ylo-1 mutant were then identified as apo-4'-lycopenal and apo-4'-lycopenol, pointing to the former as the YLO-1 substrate and indicating that cyclization is the last step in neurosporaxanthin biosynthesis. This was further substantiated by analyses of a cyclase-deficient al-2 mutant, revealing the accumulation of apo-4'-lycopenoic acid. The three acyclic apocarotenoids presented here have not been found naturally before.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biosynthetic Pathways*
  • Carotenoids / biosynthesis*
  • Carotenoids / genetics
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • Gene Expression Regulation, Fungal
  • Lactones / metabolism
  • Mutation*
  • Neurospora crassa / enzymology
  • Neurospora crassa / genetics*
  • Neurospora crassa / metabolism*


  • Fungal Proteins
  • Lactones
  • lycoperdic acid
  • neurosporaxanthin
  • Carotenoids