Glycosylation of terpenes with a substrate-flexible recombinant glycosyltransferase from Micromonospora inoyensis NRRL 3292

Abstract

Glycosyltransferase (GT)-specific degenerate PCR screening of the established fosmid libraries of the soil actinomycete Micromonospora inoyensis NRRL 3292, followed by in silico sequencing of target clones, allowed us to isolate members of the family 1 GT-encoding gene. A recombinant MiTGT, as a His-tagged protein, was heterologously expressed in Escherichia coli. Its bio-catalytic reactions with both natural terpene aglycones derived from natural sweeteners including stevioside and mogroside (as glycosyl acceptors) and nucleotide-activated hexoses (as glycosyl donors) created a number of structurally diversified terpene glycosides, thus characterizing MiTGT as a terpene glycosyltransferase with substrate-flexibility. Chromatographic isolation of the product glycosides followed by the instrumental analyses, clearly confirmed the previously unprecedented stereospecific glycosides as steviol-13-O-α-glucoside, steviol-13-O-α-(2′-deoxy)glucoside and steviol-13-O-α-galactoside, mogrol-3-O-α-glucoside, mogrol-3-O-α-(2′-deoxy)glucoside, mogrol-3-O-α-galactoside. Moreover, their elastase inhibitory activities together with anti-proliferative activities against the human pancreatic adenocarcinoma cell line PANC-1 were further investigated, hence representing the cosmeceutical and pharmaceutical potentials of the designated terpene glycosides. This is the first report on the microbe-origin bio-catalytic production of unnatural terpene α-configured glycosides.