Novel apocarotenoid intermediates in Neurospora crassa mutants imply a new biosynthetic reaction sequence leading to neurosporaxanthin formation.
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.
Estrada
Alejandro F
AF
Department of Genetics, Faculty of Biology, University of Seville, E-41012 Seville, Spain.
Maier
Dominic
D
Scherzinger
Daniel
D
Avalos
Javier
J
Al-Babili
Salim
S
D053898:Biosynthetic Pathways; D002338:Carotenoids / Q000096:biosynthesis* / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D007783:Lactones / Q000378:metabolism; D009154:Mutation; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*
D005656:Fungal Proteins; D007783:Lactones; C526725:lycoperdic acid; C471814:neurosporaxanthin; D002338:Carotenoids