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Publikation

Brandt, W.; Schulze, E.; Liberman-Aloni, R.; Bartelt, R.; Pienkny, S.; Carmeli-Weissberg, M.; Frydman, A.; Eyal, Y.; Structural modeling of two plant UDP-dependent sugar-sugar glycosyltransferases reveals a conserved glutamic acid residue that is a hallmark for sugar acceptor recognition Journal of Structural Biology 213, 107777, (2021) DOI: 10.1016/j.jsb.2021.107777

Glycosylation is one of the common modifications of plant metabolites, playing a major role in the chemical/biological diversity of a wide range of compounds. Plant metabolite glycosylation is catalyzed almost exclusively by glycosyltransferases, mainly by Uridine-diphosphate dependent Glycosyltransferases (UGTs). Several X-ray structures have been determined for primary glycosyltransferases, however, little is known regarding structure–function aspects of sugar-sugar/branch-forming O-linked UGTs (SBGTs) that catalyze the transfer of a sugar from the UDP-sugar donor to an acceptor sugar moiety of a previously glycosylated metabolite substrate.In this study we developed novel insights into the structural basis for SBGT catalytic activity by modelling the 3d-structures of two enzymes; a rhamnosyl-transferase Cs1,6RhaT – that catalyzes rhamnosylation of flavonoid-3-glucosides and flavonoid-7-glucosides and a UGT94D1 – that catalyzes glucosylation of (+)-Sesaminol 2-O-β-Dglucoside at the C6 of the primary sugar moiety.Based on these structural models and docking studies a glutamate (E290 or E268 in Cs1,6RhaT or UGT94D1, respectively) and a tryptophan (W28 or W15 in Cs1,6RhaT or UGT94D1, respectively) appear to interact with the sugar acceptor and are suggested to be important for the recognition of the sugar-moiety of the acceptorsubstrate.Functional analysis of substitution mutants for the glutamate and tryptophan residues in Cs1,6RhaT further support their role in determining sugar-sugar/branch-forming GT specificity.Phylogenetic analysis of the UGT family in plants demonstrates that the glutamic-acid residue is a hallmark of SBGTs that is entirely absent from the corresponding position in primary UGTs.
Bücher und Buchkapitel

Wessjohann, L. A.; Bartelt, R.; Brandt, W.; Natural and Nature-Inspired Macrocycles: A Chemoinformatic Overview and Relevant Examples (Marsault, E. & Peterson, M. L., eds.). 77-100, (2017) ISBN: 978-1-11909-259-9 DOI: 10.1002/9781119092599.ch4

This chapter discusses theoretical analyses and experimental studies of biologically and medicinally relevant macrocyclic compounds (MCs). The most important groups of macrocyclic natural products—excluding cyclopeptides—are discussed on the basis of selected examples. A common principle in the biosynthesis of most natural MCs is the primary synthesis of a linear precursor, followed by macrocyclization. Modification of the MC then leads to the final natural product. The chapter also focuses on the aspects of structure‐activity relationships (SAR) of macrocycles derived from chemoinformatic analyses and related theoretical methods. It further reviews the few examples that clearly show how chemoinformatics and modeling techniques, such as docking studies, can contribute essential information for drug design to improve their properties (mostly bioavailability or potency) and help to analyze and understand SAR of MCs. Finally, the chapter explores known aspects of quantitative SAR (QSAR) related to anticancer activities, antibiotics, HIV treatments, and other diseases.
Publikation

Piechulla, B.; Bartelt, R.; Brosemann, A.; Effmert, U.; Bouwmeester, H.; Hippauf, F.; Brandt, W.; The α-Terpineol to 1,8-Cineole Cyclization Reaction of Tobacco Terpene Synthases Plant Physiol. 172, 2120-2131, (2016) DOI: 10.1104/pp.16.01378

Flowers of Nicotiana species emit a characteristic blend including the cineole cassette monoterpenes. This set of terpenes is synthesized by multiproduct enzymes, with either 1,8-cineole or α-terpineol contributing most to the volatile spectrum, thus referring to cineole or terpineol synthase, respectively. To understand the molecular and structural requirements of the enzymes that favor the biochemical formation of α-terpineol and 1,8-cineole, site-directed mutagenesis, in silico modeling, and semiempiric calculations were performed. Our results indicate the formation of α-terpineol by a nucleophilic attack of water. During this attack, the α-terpinyl cation is stabilized by π-stacking with a tryptophan side chain (tryptophan-253). The hypothesized catalytic mechanism of α-terpineol-to-1,8-cineole conversion is initiated by a catalytic dyad (histidine-502 and glutamate-249), acting as a base, and a threonine (threonine-278) providing the subsequent rearrangement from terpineol to cineol by catalyzing the autoprotonation of (S)-(−)-α-terpineol, which is the favored enantiomer product of the recombinant enzymes. Furthermore, by site-directed mutagenesis, we were able to identify amino acids at positions 147, 148, and 266 that determine the different terpineol-cineole ratios in Nicotianasuaveolens cineole synthase and Nicotianalangsdorffii terpineol synthase. Since amino acid 266 is more than 10 Å away from the active site, an indirect effect of this amino acid exchange on the catalysis is discussed.
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