Enhanced transglycosylation activity of an Endo-F3 mutant by ligand-directed localization

Site- and Stereoselective Glycomodification of Biomolecules through Carbohydrate-Promoted Pictet-Spengler Reaction

Carbohydrates play pivotal roles in an array of essential biological processes and are consequently involved in many diseases. To meet the needs of glycobiology research, chemical enzymatic and non-enzymatic methods have been developed to generate glycoconjugates with well-defined structures. Herein, harnessing the unique properties of C6-oxidized glycans, we report a straightforward and robust strategy for site- and stereoselective glycomodification of biomolecules with N-terminal tryptophan residues by a carbohydrate-promoted Pictet-Spengler reaction, which is not adapted to typical aldehyde substrates under biocompatible conditions. This method reliably delivers highly homogeneous glycoconjugates with stable linkages and thus has great potential for functional modulation of peptides and proteins in glycobiology research. Moreover, this reaction can be performed at the glycosites of glycopeptides, glycoproteins and living-cell surfaces in a site-specific manner. Control experiments indicated that the protected α-O atom of aldehyde donors and free N-H bond of the tryptamine motif are crucial for this reaction. Mechanistic investigations demonstrated that the reaction exhibited a first-order dependence on both tryptophan and glycan, and deprotonation/rearomatization of the pentahydro-β-carbolinium ion intermediate might be the rate-determining step.

Recent advances in antibody glycoengineering for the gain of functions

Glycans play important roles in antibody functions, and antibody glycoengineering has long been an important research field. Here, we summarize the significant strategies of antibody glycoengineering, including expressed antibody glycoengineering in mammalian cell expression systems, chemo-enzymatic antibody glycoengineering, and yeast expression system-based antibody engineering, as well as the applications of glycoengineering in antibody-drug conjugates. These advances in antibody glycoengineering will provide a comprehensive understanding and inspire us to develop more advanced techniques to achieve glycoengineered antibodies.

Enhanced antibody-defucosylation capability of α-L-fucosidase by proximity-based protein fusion

Up to date, the reported fucosidases generally show poor activities toward the IgG core-fucose, which limits the efficiency of ENGase-catalyzed glycoengineering process. However, EndoS or EndoS2 owns excellent activity and great selectivity towards the N-glycosylation of IgGs, and their non-catalytic domains are deduced to have specific interactions to IgG Fc domain that result in the great activity and selectivity. Herein, we constructed a series fusion protein of AlfC (an α-l-fucosidase from Lactobacillus casei BL23) with EndoS/S2 non-catalytic domain by replacing the catalytic GH (glycan hydrolase) domain of EndoS/S2 with the AlfC. We found that all these fused AlfCs showed significantly enhanced defucosylation activity toward the deglycosylated IgGs (Fucα1,6GlcNAc-IgG). We also performed the kinetic study of these fusion enzymes, and our results tend to tell that the EndoS-based fusion proteins have higher k_cat values while the EndoS2-based ones possess lower K_m values other than higher k_cat. Conclusively, our research provides an effective approach to improve the activity of AlfC and remarkably shortened the defucosylation process within several minutes, which will significantly promote the development of glycoengineered antibodies in the future.

ez-ADiCon: A novel glyco-remodeling based strategy that enables preparation of homogenous antibody-drug conjugates via one-step enzymatic transglycosylation with payload-preloaded bi-antennary glycan complexes

The conserved N-linked glycan at the Fc domain of recombinant monoclonal antibodies is an attractive target for site-specific payload conjugation for preparation of homogenous antibody-drug conjugates (ADCs). Here, we report a novel ADC constructing strategy, named "ez-ADiCon", that is achieved by one-step enzymatic transglycosylation of a payload-preloaded bi-antennary glycan oxazoline onto a deglycosylated antibody. In this method, a mixture of different glycoforms of the Fc-glycan is replaced with a pre-defined payload-linked glycan. Since two payloads are linked on each donor glycan substrate, efficient conjugation results in a highly homogenous ADC with mostly-four drug molecules per antibody, facilitating hydrophobic interaction chromatography analysis and purification. We validated this conjugation strategy using Monomethyl auristatin E (MMAE) and an anti-Human epidermal growth factor receptor 2 (anti-Her2) antibody as the model ADC components and demonstrated its target-specific in vitro cytotoxicity. Our novel conjugation strategy, ez-ADiCon, provides a new approach for the preparation of next generation ADCs.