Characterization of sterol glucosyltransferase from Salinispora tropica CNB-440: Potential enzyme for the biosynthesis of sitosteryl glucoside

A sterol glucosyltransferase-encoded gene was isolated from Salinispora tropica CNB-440, a marine, sediment-dwelling, Gram positive bacterium that produces the potent anticancer compound, salinosporamide A. The full-length gene consists of 1284 nucleotides and encodes 427 amino acids with a calculated mass of 45.65 kDa. The gene was then cloned and heterologously expressed in Escherichia coli BL21(DE3). The amino acid sequence shares 39% similarity with the glycosyltransferase from Withania somnifera, which belongs to glycosyltransferase family 1. Enzyme reactions were carried out with the various free sterols (acceptor) and NDP-sugars (donor). The purified protein only showed activity for glucosylation of β-sitosterol with UDP-D-glucose and TDP-D-glucose donors, and optimal activity at pH 7.5 and 37 °C. Among these two donors, UDP-D-glucose was preferred.