Biochemical characterization of recombinant UDP-glucose: sterol 3-O-glycosyltransferase from Micromonospora rhodorangea ATCC 31603 and enzymatic biosynthesis of sterol-3-O-β-glucosides.

A uridine diphosphate-glucose: sterol glycosyltransferase-encoding gene was isolated and cloned from the established fosmid library of Micromonospora rhodorangea ATCC 27932 that usually produces the aminoglycoside antibiotic geneticin. The gene consists of 1,185 base pairs and encodes a 41.4 kDa protein, which was heterologously expressed in Escherichia coli BL21(DE3). In silico analyses of the deduced gene product suggested that it is a member of the family 1 glycosyltransferases. The recombinant protein MrSGT was able to catalyze the transfer of a glucosyl moiety onto the C-3 hydroxy function in sterols (beta-sitosterol, campesterol, and cholesterol), resulting in the corresponding steryl glucosides (beta-sitosterol-3O-beta-D-glucoside, campesterol-3-O-beta-D-glucoside, and cholesterol-3-O-beta-D-glucoside). This enzyme prefers phytosterols to cholesterol, and also shows substrate flexibility to some extent, in that it could recognize a number of acceptor substrates.