Structural and functional studies of plant natural product uridine diphosphate glycosyltransferases

Glycosylation of small molecules plays key roles in many biological processes and is a key factor in determining chemical complexity and diversity in plants. Uridine diphosphate glycosyltransferases (UGTs) are the central players of the glycosylation processes. We determined three plant small molecule GT structures, i.e. for UGT71G1, UGT85H2 and UGT78G1 from Medicago truncatula, and provided the structural insight into UGTs and the glycosylation mechanism of small molecules. These structures revealed the detailed interactions between enzymes and substrates, which define the substrate specificity of individual enzymes. Structural comparison showed that their three dimensional structures are highly conserved although they share relatively low sequence identities. They share a similar binding mode with sugar donor and have a conserved catalytic mechanism with a highly conserved histidine residue (His22 in UGT71G1) as the catalytic base. Comparison also revealed some potential conformational changes when substrates bind to the enzyme. The recently solved structure of UGT78G1 complexed with both UDP and acceptor substrate myricetin sheds light on its unique de-glycosylation activity.

Structure-based mutagenesis studies on UGT71G1 and UGT85H2 showed that we were able to manipulate the regio-selectivity of glycosylation, and improve the enzyme activity and quality by site-directed mutations. Overall, our study greatly advanced our understanding of the glycosylation mechanisms and the complex substrate/product specificity, and opened up new opportunities to engineer and manipulate the biosynthesis of plant natural products.

Publications:
Wang, X. Structure, mechanism and engineering of plant natural product glycosyltransferases. FEBS Letters (2009), 583, 3303-3309.

Modolo, L.V., Li, L., Dixon, R.A., Wang, X. Crystal structures of glycosyltransferase UGT78G1 reveal the molecular basis for glycosylation and deglycosylation of isoflavonoids. J. Mol. Biol. (2009), 392, 1292-1302.

Modolo, L.V., Escamilla-Trevino, L.L., Dixon, R.A., Wang, X. Single amino acid mutations of Medicago glycosyltransferase UGT85H2 enhance activity and impart reversibility. FEBS Letters (2009), 583, 2131-2135.

Li, L., Modolo, L.V., Escamilla-Trevino L.L., Achnine, L., Dixon, R.A., and Wang, X. Crystal structure of Medicago truncatula UGT85H2 - Insights into the structural basis of a multifunctional (iso)flavonoid glycosyltransferase. J. Mol. Biol. (2007), 370, 951-963.

Modolo, L.V., Blount, J.W., Achnine, L., Naoumkina, M.A., Wang, X., and Dixon, R.A. A functional genomics approach to (iso)flavonoid glycosylation in the model legume Medicago truncatula. Plant Molecular Biology (2007), 64, 499-518.

He, X., Wang, X., and Dixon, R.A. Mutational analysis of the Medicago glycosyltransferase UGT71G1 reveals residues that control regio-selectivity for (iso)flavonoid glycosylation. J. Biol. Chem. (2006), 281, 34441-34447.

Shao, H., He, X., Achnine, L., Blount, J.W., Dixon, R.A., and Wang, X. Crystal structures of a multifunctional triterpene/flavonoid glycosyltransferase from Medicago truncatula. Plant Cell (2005) Nov; 17(11): 3141-54.

Acknowledgment and Disclaimer:
This material is based upon work supported by the National Science Foundation under Grant No. 0416883. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.