title: Kinetic studies on recombinant UDP-glucose: sterol 3-O-β-glycosyltransferase from Micromonospora rhodorangea and its bioconversion potential.
abstract: Kinetics of a recombinant uridine diphosphate-glucose: sterol glycosyltransferase from Micromonospora rhodorangea ATCC 27932 (MrSGT) were studied using a number of sterols (including phytosterols) as glycosyl acceptors. The lowest K m value and the highest catalytical efficiency (k cat/K m) were found when β-sitosterol was the glycosyl acceptor in the enzymatic reaction. In contrast to the enzyme's flexibility toward the glycosyl acceptor substrate, this recombinant enzyme was highly specific to uridine diphosphate (UDP)-glucose as the donor substrate. Besides, the UDP-glucose-dependent MrSGT was able to attach one glucose moiety specifically onto the C-3 hydroxyl group of other phytosterols such as fucosterol and gramisterol, yielding stereo-specific fucosterol-3-O-β-D-glucoside and gramisterol-3-O-β-D-glucoside, respectively. Based on kinetic data obtained from the enzyme's reactions using five different sterol substrates, the significance of the alkene (or ethylidene) side chains on the C-24 position in the sterol scaffolds was described and the possible relationship between the substrate structure and enzyme activity was discussed. This is the first report on the enzymatic bioconversion of the above two phytosteryl 3-O-β-glucosides, as well as on the discovery of a stereospecific bacterial SGT which can attach a glucose moiety in β-conformation at the C-3 hydroxyl group of diverse sterols, thus highlighting the catalytic potential of this promiscuous glycosyltransferase to expand the structural diversity of steryl glucosides.
authors.affiliation: Department of Biotechnology Convergent Pharmaceutical Engineering, SunMoon University, Asan, Chungnam, 31460, Republic of Korea.
authors.forename: Nguyen Huu
authors.initials: NH
authors.lastname: Hoang
authors.affiliation: Department of Biotechnology Convergent Pharmaceutical Engineering, SunMoon University, Asan, Chungnam, 31460, Republic of Korea.
authors.forename: Nguyen Lan
authors.initials: NL
authors.lastname: Huong
authors.affiliation: School of Biosystem and Biomedical Science, Korea University, Seoul, 02841, Republic of Korea.
authors.forename: Byul
authors.initials: B
authors.lastname: Kim
authors.affiliation: School of Biosystem and Biomedical Science, Korea University, Seoul, 02841, Republic of Korea. jewonpark@korea.ac.kr.
authors.forename: Je Won
authors.initials: JW
authors.lastname: Park
keywords: Catalytic promiscuity; Fucosterol-3-O-β-D-glucoside; Gramisterol-3-O-β-D-glucoside; Kinetics; UDP-glucose sterol glycosyltransferase