Abstract
Xanthophyllomyces dendrorhous synthesizes astaxanthin, a carotenoid used in aquaculture. Astaxanthin is synthesized from metabolites of the mevalonate pathway, which are also precursors for sterols biosynthesis. The interruption of the CYP61 gene, which is involved in the synthesis of ergosterol (mutant CBS.cyp61–), resulted in a phenotype that overproduces carotenoids due to the activation of the SREBP pathway. In this work, we constructed other mutants of ergosterol biosynthesis in this yeast to evaluate whether they have the same phenotype as mutant CBS.cyp61–. By bioinformatic analysis, the ERG3 and ERG4 genes of X. dendrorhous were identified, and each gene was deleted in the wild-type strain. Mutants CBS.Δerg3 and CBS.Δerg4 did not produce ergosterol; CBS.Δerg3 primarily accumulated episterol, and CBS.Δerg4 primarily accumulated ergosta-5,7,22,24(28)-tetraenol. The transcription levels of the HMGS gene of the mevalonate pathway were evaluated by RT-qPCR, which showed a slight increase in CBS.Δerg4, but the transcription levels were still 10-fold lower than in strain CBS.cyp61–. Both CBS.Δerg3 and CBS.Δerg4 did not overproduce carotenoids, even though they do not produce ergosterol. Thus, the results of this study indicate that the absence of ergosterol does not activate the SREBP pathway in X. dendrorhous, but rather it depends on other alterations in sterol composition.
Highlights
Xanthophyllomyces dendrorhous is a basidiomycete yeast that produces carotenoids, which are natural liposoluble pigments of 40 carbon atoms that exhibit shades ranging from yellow to red (Golubev, 1995) and have antioxidant properties attributed to their structure (Guerin et al, 2003)
X. dendrorhous ERG3 and ERG4 Genes In X. dendrorhous, the biosynthesis of astaxanthin begins with the condensation of dimethylallyl-pyrophosphate (DMAPP, C5) and isopentenyl-pyrophosphate (IPP, C5) (Figure 1), which are synthesized through the mevalonate (MVA) pathway, producing geranyl-pyrophosphate (GPP, C10)
It was predicted that the encoded proteins would be located at the endoplasmic reticulum, which is consistent with their function as in S. cerevisiae, the ergosterol biosynthesis ends in this organelle (Nishino, 1981)
Summary
Xanthophyllomyces dendrorhous is a basidiomycete yeast that produces carotenoids, which are natural liposoluble pigments of 40 carbon atoms that exhibit shades ranging from yellow to red (Golubev, 1995) and have antioxidant properties attributed to their structure (Guerin et al, 2003). A second IPP molecule is added, giving rise to farnesyl-pyrophosphate (FPP, C15), which is a substrate for both sterol and carotenoid synthesis. Two FPP molecules are condensed, giving squalene, and in the synthesis of carotenoids, FPP is joined to a third molecule of IPP, giving geranylgeranyl-pyrophosphate (GGPP, C20). The condensation of two molecules of GGPP gives phytoene (the first carotenoid of the synthesis pathway), which is transformed into lycopene through four desaturation steps. The cyclization of both ends of lycopene produces β-carotene, and the addition of a keto and a hydroxyl to both terminal rings of β-carotene gives astaxanthin (Loto et al, 2012)
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