A novel glucosyltransferase from Catharanthus roseus cell suspensions

The potential applications of glycosyltransferases in glycoconjugate synthesis have attracted considerable interest from the biotechnology community in recent years. In this work, we present a novel glucosyltransferase from Catharanthus roseus cell cultures. The enzyme was purified to one spot in SDS-polyacrylamide gel electrophoresis, and its molecular weight was about 51 kDa. The optimum temperature was 35 °C, and the optimum pH was 7.6. Sodium ion has weak effect on enzyme activity, whereas divalent ions inhibit enzyme activity strongly. The Km values were 0.112, 0.077, 0.064 and 1.0 mM for scopoletin, 5,7-dihydroxyflavone, 5,7-dihydroxyflavanone and UDPG, respectively. Substrate screening with the purified enzyme was performed against a range of phenolic compounds using UDPG as sugar donor. The enzyme showed activity towards a number of coumarins including umbelliferone, scopoletin, isoscopoletin and esculetin, and flavonoids including a flavone, a flavanone and chalcones. No activity was detected with compounds characterized by a single aromatic ring, i.e. simple and acidic phenols. The substrate specificity and the regioselectivity suggest enzyme structural features that are different from those of other glucosyltransferases.