earticle

영어

Glycosylation of plant secondary metabolites is mediated by family 1 glycosyltransferase, called uridine-diphosphate (UDP)-dependent glycosyltransferase (UGT). The N-terminal of UGT recognizes the sugar acceptor and the C-terminal interacts with the sugar-donor. Molecular basis of selection of sugar donor in UGT is not clear. UGT78D2 from Arabidopsis thaliana (AtUGT78D2) transfers a glucose group of UDP-glucose to 3-hydroxyl group of quercetin. On the other hand, the other UGT (ATUGT78D3), which showed 80 % amino acid identity to AtUGT78D2, uses UDP-arabinose as a sugar donor to make quercetin 3-O-arabinodise. Analysis of sugar binding site reveals that five amino acids are different between two UGTs. To find out which amino acid affects to their UDP-sugar donor selectivity, site-directed mutagenesis was performed. One amino acid at the C-terminal of AtUGT78D3 turned out to be critical for the selectionof UDP-sugar. With modeled structures of two AtUGT followed by site-directed mutagenesis, structural basis of UDP-selectivity in UDP-dependent glycosyltransferase is elucidated. Alternation of regioselectivity of UGTs is also challenging area. In order to alter the regioselelctivity, PGT-3 was used. PGTs uses quercetin as substrate and transferrs a glucose to the 4’ hydroxyl group. However, PGT-3 transferred a glucose group to the 3-hydroxyl group of isorhamnetin. Molecular modeling and docking and site directed mutagenesis were carried out to engineer a PGT-3 having a specificity for isorhamnetin but not for quercetin. The engineered PGT-3 that have exclusive activity toward isorhamnetin will be described.