Abstract
Carminic acid, a glucosylated anthraquinone found in scale insects like Dactylopius coccus, has since ancient times been used as a red colorant in various applications. Here we show that a membrane-bound C-glucosyltransferase, isolated from D. coccus and designated DcUGT2, catalyzes the glucosylation of flavokermesic acid and kermesic acid into their respective C-glucosides dcII and carminic acid. DcUGT2 is predicted to be a type I integral endoplasmic reticulum (ER) membrane protein, containing a cleavable N-terminal signal peptide and a C-terminal transmembrane helix that anchors the protein to the ER, followed by a short cytoplasmic tail. DcUGT2 is found to be heavily glycosylated. Truncated DcUGT2 proteins synthesized in yeast indicate the presence of an internal ER-targeting signal. The cleavable N-terminal signal peptide is shown to be essential for the activity of DcUGT2, whereas the transmembrane helix/cytoplasmic domains, although important, are not crucial for its catalytic function.
Highlights
Carminic acid, a glucosylated anthraquinone found in scale insects like Dactylopius coccus, has since ancient times been used as a red colorant in various applications
Copious amounts of Carminic acid (CA) are present in adult female cochineals and it was assumed that genes encoding enzymes involved in the biosynthesis of this red pigment would be highly expressed at this life stage
No product formation was detected in the liquid chromatography-mass spectrometry (LC-MS) and thin-layer chromatography (TLC) profiles following incubation with UDP-glucose or [14C]UDP-glucose, respectively, and using the putative substrates flavokermesic acid (FK) and kermesic acid (KA)
Summary
A glucosylated anthraquinone found in scale insects like Dactylopius coccus, has since ancient times been used as a red colorant in various applications. Carminic acid (CA) is a natural red pigment found in some scale insects including the American cochineals (Dactylopius coccus Costa), which are native to tropical and subtropical regions of South America and Mexico. These scale insects are mostly sessile phloem feeders, living as parasites exclusively on cacti belonging to the Opuntia genus. CA may be further purified by precipitation with alum under acidic conditions to produce a more intense red aluminum salt called carmine lake This carmine lake is essentially water and acid insoluble, water-soluble forms have been generated for applications demanding lower pH7. CA has gained renewed popularity as a safe colorant with superior stability
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