Expression and structural characterization of a baculovirus ecdysteroid UDP-glucosyltransferase

The baculovirus enzyme ecdysteroid UDP-glucosyltransferase (EGT) disrupts the hormonal balance of the insect host by catalysing the conjugation of ecdysteroids, the moulting hormones, with the sugar moiety from UDP-glucose or UDP-galactose. In this study, EGT has been overproduced using a recombinant Autographa californica nucleopolyhedrovirus and an antiserum has been raised against the purified protein. This antiserum was used to visualize the kinetics of expression of EGT by wild-type AcMNPVL-1 and by the overproducing recombinant virus. The inclusion of tunicamycin during these time-course experiments suggested that EGT is glycosylated. This was confirmed by Endo F treatment, which showed that glycosylation increased the apparent subunit molecular mass by approximately 11 kDa. These sugars do not appear to be required for enzyme activity. EGT activity invariantly elutes from gel-filtration columns as a single peak corresponding to a 260 kDa (+/-50 kDa) protein. This suggests that the enzyme is an oligomer of three to five subunits, since the subunit molecular mass is 56 kDa.