Structural Characterization of O‐ and C‐Glycosylating Variants of the Landomycin Glycosyltransferase LanGT2

The structures of the O‐glycosyltransferase LanGT2 and the engineered, C? C bond‐forming variant LanGT2S8Ac show how the replacement of a single loop can change the functionality of the enzyme. Crystal structures of the enzymes in complex with a nonhydrolyzable nucleotide‐sugar analogue revealed that there is a conformational transition to create the binding sites for the aglycon substrate. This induced‐fit transition was explored by molecular docking experiments with various aglycon substrates.     

Chemoenzymatic Assembly of Mammalian O‐Mannose Glycans

O‐Mannose glycans account up to 30 % of total O‐glycans in the brain. Previous synthesis and functional studies have only focused on the core M3 O‐mannose glycans of α‐dystroglycan, which are a causative factor for various muscular diseases. In this study, a highly efficient chemoenzymatic strategy was developed that enabled the first collective synthesis of 63 core M1 and core M2 O‐mannose glycans. This chemoenzymatic strategy features the gram‐scale chemical synthesis of five judiciously designed core structures, and the diversity‐oriented modification of the core structures with three enzyme modules to provide 58 complex O‐mannose glycans in a linear sequence that does not exceed four steps. The binding profiles of synthetic O‐mannose glycans with a panel of lectins, antibodies, and brain proteins were also explored by using a printed O‐mannose glycan array.     

Plant glycosyltransferases: their potential as novel biocatalysts

The potential application of glycosyltransferases in glycoconjugate synthesis has attracted considerable interest from the biotechnology community in recent years. This concept article focuses on the current understanding of the chemistry of a family of plant enzymes capable of glycosylating small lipophilic molecules. These enzymes are discussed in terms of their regio- and enantioselective substrate recognition, sugar-donor selectivity and their utility as biocatalysts in whole-cell systems.     

Preparation of Well‐Defined Antibody–Drug Conjugates through Glycan Remodeling and Strain‐Promoted Azide–Alkyne Cycloadditions

Antibody–drug conjugates hold considerable promise as anticancer agents, however, producing them remains a challenge and there is a need for mild, broadly applicable, site‐specific conjugation methods that yield homogenous products. It was envisaged that enzymatic remodeling of the oligosaccharides of an antibody would enable the introduction of reactive groups that can be exploited for the site‐specific attachment of cytotoxic drugs. This is based on the observation that glycosyltransferases often tolerate chemical modifications in their sugar nucleotide substrates, thus allowing the installation of reactive functionalities. An azide was incorporated because this functional group is virtually absent in biological systems and can be reacted by strain‐promoted alkyne–azide cycloaddition. This method, which does not require genetic engineering, was used to produce an anti‐CD22 antibody modified with doxorubicin to selectively target and kill lymphoma cells.     

A Glycan Array‐Based Assay for the Identification and Characterization of Plant Glycosyltransferases

Growing plants with modified cell wall compositions is a promising strategy to improve resistance to pathogens, increase biomass digestibility, and tune other important properties. In order to alter biomass architecture, a detailed knowledge of cell wall structure and biosynthesis is a prerequisite. We report here a glycan array‐based assay for the high‐throughput identification and characterization of plant cell wall biosynthetic glycosyltransferases (GTs). We demonstrate that different heterologously expressed galactosyl‐, fucosyl‐, and xylosyltransferases can transfer azido‐functionalized sugar nucleotide donors to selected synthetic plant cell wall oligosaccharides on the array and that the transferred monosaccharides can be visualized “on chip” by a 1,3‐dipolar cycloaddition reaction with an alkynyl‐modified dye. The opportunity to simultaneously screen thousands of combinations of putative GTs, nucleotide sugar donors, and oligosaccharide acceptors will dramatically accelerate plant cell wall biosynthesis research.     

Synthesis of saccharide precursors for preparation of potential inhibitors of glycosyltranferases

Ethyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Va), its β-analog (Vb); as well as benzyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Xa) and its β-analog (Xb), having an unprotected OH group at C-1, were prepared by sequential synthesis starting from commercially available D-fructose. These compounds represent suitable nucleophiles for the preparation of model carbohydrate mimetics of a glycosyltransferase inhibitor type in transition state. The structures of all compounds were confirmed by NMR spectral data and elemental analyses.