Characterization of a novel crocetin glycosyltransferase UGTCs4 involved in two steps of glycosylation in crocin biosynthesis from crocus cultured cell

Abstract crocins, water-soluble apocarotenoids, are a kind of crocetin glucosyl-esters that are due to the action of glycosyltransferases that are added glucose moieties to crocetin. To date, the glycosyltransferases involved in crocin biosynthesis are gradually discovered in the plant kingdom. In this work, a putative crocetin glycosyltransferase UGTCs4was first functionally characterized from cultured crocus cells. The constructed model of UGTCs4 based on the given model of UGT75L2 showed that highly structural similarity with that of UGT75L6 and UGT74AD1, suggesting a common function specializing in glycosylation of the glucose moieties of crocetin glucosides. Function characterization demonstrated that UGTCs4 could glycosylate crocetin yielding crocetin-monoglycoside(crocin 5) and crocetin-diglycoside(crocin 3) which were produced in a time-dependent manner. This work represents, to our knowledge, the first functional identification of a C. sativus crocetin glycosyltransferase involved in the crocin biosynthetic pathway employing the purified recombinant protein.