Transglycosylation Activity of Glycosynthase Mutants of Endo-β-N-Acetylglucosaminidase from Coprinopsis cinerea

Chemical and Chemoenzymatic Synthesis of Peptide and Protein Therapeutics Conjugated with Human N-Glycans

Glycosylation is one of the most ubiquitous post-translational modifications. It affects the structure and function of peptides/proteins and consequently has a significant impact on various biological events. However, the structural complexity and heterogeneity of glycopeptides/proteins caused by the diversity of glycan structures and glycosylation sites complicates the detailed elucidation of glycan function and hampers their clinical applications. To address these challenges, chemical and/or enzyme-assisted synthesis methods have been developed to realize glycopeptides/proteins with well-defined glycan morphologies. In particular, N-glycans are expected to be useful for improving the solubility, in vivo half-life and aggregation of bioactive peptides/proteins that have had limited clinical applications so far due to their short duration of action in the blood and unsuitable physicochemical properties. Chemical glycosylation performed in a post-synthetic procedure can be used to facilitate the development of glycopeptide/protein analogues or mimetics that are superior to the original molecules in terms of physicochemical and pharmacokinetic properties. N-glycans are used to modify targets because they are highly biodegradable and biocompatible and have structures that already exist in the human body. On the practical side, from a quality control perspective, close attention should be paid to their structural homogeneity when they are to be applied to pharmaceuticals.

Synthesis of a fluorescent probe for measuring the activity of endo-β-N-acetylglucosaminidases recognizing hybrid-type N-glycans

A fluorescence-quenching-based assay system was constructed to determine the hydrolytic activity of endo-β-N-acetylglucosaminidases (ENGases) interacting with hybrid-type N-glycans. This was achieved using a dual-labeled fluorescent probe with a nonasaccharide structure. We produced the nonasaccharide skeleton by the stepwise glycosylation of the galactose residue on a galactosyl chitobiose derivative. Next, we introduced azido and acetoxy groups into the nonasaccharide derivative in a stepwise manner, which led to stereochemistry inversion at both the C-4 and C-2 hydroxy groups on its galactose residue. The protecting groups of the resulting nonasaccharide derivative were removed, and the derivative was labeled with an N-methylanthraniloyl group to obtain a reporter dye and a 2,4-dinitrophenyl group as a quenching molecule to obtain target probe 1. The use of this probe along with a microplate reader enabled a facile evaluation of the hydrolytic activities of ENGases Endo-H, Endo-M, Endo-F3, Endo-S, and Endo-CC. Furthermore, this probe could also assist in the search for novel ENGases that are specific to hybrid-type N-glycans.

Rapid preparation of a glycan oxazoline and a homogeneously glycosylated antibody with an enzyme-immobilized monolithic column

Chemo-enzymatic glycan engineering is considered to be one of the most promising strategies to enhance efficiency in pharmaceutical research. However, it is assumed that this technology has limited industrial application for the production of biological therapeutics because of the high cost of the process. In this study, we developed a scheme for rapidly preparing a glycan oxazoline and a homogeneously glycosylated antibody. The enzyme-immobilized monolith and the flow chemistry-based approach enabled a glycan oxazoline and a homogeneously glycosylated antibody to be obtained at the gram scale from starting materials (sialylglycopeptide and heterogeneously glycosylated protein) within 2.5 h. This cost-effective scheme for obtaining a large amount of glycan donors and homogeneously glycosylated proteins in a short time will be helpful to implement glycan engineering technology for industrial purposes such as pharmaceutical production.

Characterization of novel endo-β-N-acetylglucosaminidases from intestinal Barnesiella intestinihominis that hydrolyze multi-branched complex-type N-glycans

Endo-β-N-acetylglucosaminidases (ENGases) are enzymes that hydrolyze N-linked glycans. Many ENGases have been characterized, but few have been identified with hydrolytic activity towards multi-branched complex-type N-glycans. In this study, three candidate ENGases were identified from Barnesiella intestinihominis based on database searches and phylogenetic analysis. A domain search identified the N x E motif in all three candidates, suggesting that they were members of glycosyl hydrolase family 85 (GH85). The three candidate ENGases, named Endo-BIN1, Endo-BIN2, and Endo-BIN3, were expressed in Escherichia coli cells, and their hydrolytic activity towards N-glycans and glycoproteins was measured by high performance liquid chromatography analysis and SDS-PAGE analysis. All ENGases showed hydrolytic activity towards glycoproteins, but only Endo-BIN2 and Endo-BIN3 showed hydrolytic activity towards pyridylaminated N-glycans. The optimum pH of Endo-BIN1, Endo-BIN2, and End-BIN3 was pH 6.5, 4.0, and 7.0, respectively. We measured substrate specificities of Endo-BIN2 and Endo-BIN3 towards pyridylaminated N-glycans, and found that the two Endo-BIN enzymes showed similar substrate specificity, preferring bi-antennary complex-type N-glycans with galactose or α2,6-linked sialic acid residues at the non-reducing ends. Endo-BIN2 and Endo-BIN3 were also able to hydrolyze multi-branched complex-type N-glycans. SDS-PAGE analysis revealed that all Endo-BIN enzymes were capable of releasing complex-type N-glycans from glycoproteins such as rituximab, transferrin, and fetuin. We expect that B. intestinihominis possesses ENGases to facilitate the utilization of complex-type N-glycans from host cells. These findings will have applications in N-glycan remodeling of glycoproteins and the development of pharmaceuticals.

LC-MS/MS-PRM Quantification of IgG Glycoforms Using Stable Isotope Labeled IgG1 Fc Glycopeptide Standard

Targeted quantification of proteins is a standard methodology with broad utility, but targeted quantification of glycoproteins has not reached its full potential. The lack of optimized workflows and isotopically labeled standards limits the acceptance of glycoproteomics quantification. In this work, we introduce an efficient and streamlined chemoenzymatic synthesis of a library of isotopically labeled glycopeptides of IgG1 which we use for quantification in an energy optimized LC-MS/MS-PRM workflow. Incorporation of the stable isotope labeled N-acetylglucosamine enables an efficient monitoring of all major fragment ions of the glycopeptides generated under the soft higher-energy C-trap dissociation (HCD) conditions, which reduces the coefficients of variability (CVs) of the quantification to 0.7-2.8%. Our results document, for the first time, that the workflow using a combination of stable isotope labeled standards with intrascan normalization enables quantification of the glycopeptides by an electron transfer dissociation (ETD) workflow, as well as the HCD workflow, with the highest sensitivity compared to traditional workflows. This was exemplified by a rapid quantification (13 min) of IgG1 Fc glycoforms from COVID-19 patients.

Catanionic Vesicles as a Facile Scaffold to Display Natural N-Glycan Ligands for Probing Multivalent Carbohydrate-Lectin Interactions

Multivalent interactions are a key characteristic of protein-carbohydrate recognition. Phospholipid-based liposomes have been explored as a popular platform for multivalent presentation of glycans, but this platform has been plagued by the instability of typical liposomal formulations in biological media. We report here the exploitation of catanionic vesicles as a stable lipid-based nanoparticle scaffold for displaying large natural N-glycans as multivalent ligands. Hydrophobic insertion of lipidated N-glycans into the catanionic vesicle bilayer was optimized to allow for high-density display of structurally diverse N-glycans on the outer membrane leaflet. In an enzyme-linked competitive lectin-binding assay, the N-glycan-coated vesicles demonstrated a clear clustering glycoside effect, with significantly enhanced affinity for the corresponding lectins including Sambucus nigra agglutinin (SNA), concanavalin A (ConA), and human galectin-3, in comparison with their respective natural N-glycan ligands. Our results showed that relatively low density of high-mannose and sialylated complex type N-glycans gave the maximal clustering effect for binding to ConA and SNA, respectively, while relatively high-density display of the asialylated complex type N-glycan provided maximal clustering effects for binding to human galectin 3. Moreover, we also observed a macromolecular crowding effect on the binding of ConA to high-mannose N-glycans when catanionic vesicles bearing mixed high-mannose and complex-type N-glycans were used. The N-glycan-coated catanionic vesicles are stable and easy to formulate with varied density of ligands, which could serve as a feasible vehicle for drug delivery and as potent inhibitors for intervening protein-carbohydrate interactions implicated in disease.

A fluorogenic probe for core-fucosylated glycan-preferred ENGase

A fluorescence-quenching-based assay system to determine the hydrolytic activity of endo-β-N-acetylglucosaminidases (ENGases), which act on the innermost N-acetylglucosamine (GlcNAc) residue of the chitobiose segment of core-fucosylated N-glycans, was constructed using a dual-labeled fluorescent probe with a hexasaccharide structure. The fluorogenic probe was evaluated using a variety of ENGases, including Endo-M W251N mutant, Endo-F3, and Endo-S, which recognize core fucosylated N-glycans. The occurrence of a hydrolysis reaction was detected by observing an increased fluorescence intensity, ultimately allowing the ENGase activities to be easily and quantitatively evaluated, with the exception of Endo-S. The obtained results clearly indicated the substrate specificities of the examined ENGases.

Identification and characterization of a novel thermo-stable endo-β-N-acetylglucosaminidase from Rhizomucorpusillus

Endo-β-N-acetylglucosaminidase (ENGase) is an enzyme that hydrolyzes the chitobiose core of N-glycans and is widely used for glycan analysis on glycoproteins and preparation of precursors for glycosylated compounds. While most of the ENGases that can hydrolyze complex-type glycans are derived from eukaryotes, their production by heterologous expression using Escherichia coli is insufficient, making the production process expensive. From an industrial perspective, there is a need for a less expensive enzyme with higher activity and stability. In this study, we identified a novel ENGase gene from a thermophilic fungus, Rhizomucor pusillus, and named it Endo-Rp. Characterization of the recombinant Endo-Rp showed that the enzyme had maximum hydrolytic activity at 60 °C and hydrolyzed high-mannose-type and biantennary complex-type glycans, but not (2,4)-branched triantennary complex-type or fucosylated glycans. Endo-Rp also hydrolyzed N-glycans attached to RNase B and human transferrin. In summary, we consider Endo-Rp to be a valuable enzyme in various scientific and industrial applications.

LC-MS/MS-PRM Quantification of IgG glycoforms using stable isotope labeled IgG1 Fc glycopeptide standard

Targeted quantification of proteins is a standard methodology with broad utility, but targeted quantification of glycoproteins has not reached its full potential. The lack of optimized workflows and isotopically labeled standards limits the acceptance of glycoproteomics quantification. In this paper, we introduce an efficient and streamlined chemoenzymatic synthesis of a library of isotopically labeled glycopeptides of IgG1 which we use for quantification in an energy optimized LC-MS/MS-PRM workflow. Incorporation of the stable isotope labeled N-acetylglucosamine enables an efficient monitoring of all major fragment ions of the glycopeptides generated under the soft collision induced dissociation (CID) conditions which reduces the CVs of the quantification to 0.7-2.8%. Our results document, for the first time, that the workflow using a combination of stable isotope labeled standards with intra-scan normalization enables quantification of the glycopeptides by an electron transfer dissociation (ETD) workflow as well as the CID workflow with the highest sensitivity compared to traditional workflows., This was exemplified by a rapid quantification (13-minute) of IgG1 Fc glycoforms from COVID-19 patients.

Graphic Abstract

Characterization of novel endo-β-N-acetylglucosaminidase from Bacteroides nordii that hydrolyzes multi-branched complex type N-glycans

Endo-β-N-acetylglucosaminidases (ENGases) are enzymes that hydrolyze the N-linked oligosaccharides. Many ENGases have already been identified and characterized. However, there are still a few enzymes that have hydrolytic activity toward multibranched complex-type N-glycans on glycoproteins. In this study, one novel ENGase from Bacteroides nordii (Endo-BN) species was identified and characterized. The recombinant protein was prepared and expressed in Escherichia coli cells. This Endo-BN exhibited optimum hydrolytic activity at pH 4.0. High performance liquid chromatography (HPLC) analysis showed that Endo-BN preferred core-fucosylated complex-type N-glycans, with galactose or α2,6-linked sialic acid residues at their non-reducing ends. The hydrolytic activities of Endo-BN were also tested on different glycoproteins from high-mannose type to complex-type oligosaccharides. The reaction with human transferrin, fetuin, and α1-acid glycoprotein subsequently showed that Endo-BN is capable of releasing multi-branched complex-type N-glycans from these glycoproteins.

General and Robust Chemoenzymatic Method for Glycan-Mediated Site-Specific Labeling and Conjugation of Antibodies: Facile Synthesis of Homogeneous Antibody-Drug Conjugates

Site-specific labeling and conjugation of antibodies are highly desirable for fundamental research and for developing more efficient diagnostic and therapeutic methods. We report here a general and robust chemoenzymatic method that permits a one-pot site-specific functionalization of antibodies. A series of selectively modified disaccharide oxazoline derivatives were designed, synthesized, and evaluated as donor substrates of different endoglycosidases for antibody Fc glycan remodeling. We found that among several endoglycosidases tested, wild-type endoglycosidase from Streptococcus pyogenes of serotype M49 (Endo-S2) exhibited remarkable activity in transferring the functionalized disaccharides carrying site-selectively modified azide, biotin, or fluorescent tags to antibodies without hydrolyzing the resulting transglycosylation products. This discovery, together with the excellent Fc deglycosylation activity of Endo-S2 on recombinant antibodies, allowed direct labeling and functionalization of antibodies in a one-pot manner without the need of intermediate and enzyme separation. The site-specific introduction of varied numbers of azide groups enabled a highly efficient synthesis of homogeneous antibody-drug conjugates (ADCs) with a precise control of the drug-to-antibody ratio (DAR) ranging from 2 to 12 via a copper-free strain-promoted click reaction. Cell viability assays showed that ADCs with higher DARs were more potent in killing antigen-overexpressed cells than the ADCs with lower DARs. This new method is expected to find applications not only for antibody-drug conjugation but also for cell labeling, imaging, and diagnosis.

Membrane traffic related to endosome dynamics and protein secretion in filamentous fungi

In eukaryotic cells, membrane-surrounded organelles are orchestrally organized spatiotemporally under environmental situations. Among such organelles, vesicular transports and membrane contacts occur to communicate each other, so-called membrane traffic. Filamentous fungal cells are highly polarized and thus membrane traffic is developed to have versatile functions. Early endosome (EE) is an endocytic organelle that dynamically exhibits constant long-range motility through the hyphal cell, which is proven to have physiological roles, such as other organelle distribution and signal transduction. Since filamentous fungal cells are also considered as cell factories, to produce valuable proteins extracellularly, molecular mechanisms of secretory pathway including protein glycosylation have been well investigated. In this review, molecular and physiological aspects of membrane traffic especially related to EE dynamics and protein secretion in filamentous fungi are summarized, and perspectives for application are also described.

Innovative Preparation of Biopharmaceuticals Using Transglycosylation Activity of Microbial Endoglycosidases

Most functional biopharmaceuticals such as antibodies are glycoproteins carrying N-linked oligosaccharides (N-glycans). In animal cells, these glycans are generally expressed as heterogeneous glycoforms that are difficult to separate into a pure form. The structure of these glycans directly affects several biological aspects of the glycoproteins, especially binding affinity. Therefore, the preparation of glycoproteins with well-defined and homogeneous glycoforms is necessary for functional studies and improved efficacy, particularly for biopharmaceuticals. This review describes the recent remarkable progress in the development and production of biopharmaceutical glycan-modified antibodies, through the use of glycan remodeling using microbial endoglycosidases and sophisticated glycoengineering techniques utilizing microbial enzymatic reaction mechanisms.

Structural insights into the mechanisms and specificities of IgG-active endoglycosidases

The conserved N-glycan on Asn297 of immunoglobulin G (IgG) has significant impacts on antibody effector functions, and is a frequent target for antibody engineering. Chemoenzymatic synthesis has emerged as a strategy for producing antibodies with homogenous glycosylation and improved effector functions. Central to this strategy is the use of enzymes with activity on the Asn297 glycan. EndoS and EndoS2, produced by Streptococcus pyogenes, are endoglycosidases with remarkable specificity for Asn297 glycosylation, making them ideal tools for chemoenzymatic synthesis. Although both enzymes are specific for IgG, EndoS2 recognizes a wider range of glycans than EndoS. Recent progress has been made in understanding the structural basis for their activities on antibodies. In this review, we examine the molecular mechanism of glycosidic bond cleavage by these enzymes and how specific point mutations convert them into glycosynthases. We also discuss the structural basis for differences in the glycan repertoire that IgG-active endoglycosidases recognize, which focuses on the structure of the loops within the glycoside hydrolase (GH) domain. Finally, we discuss the important contributions of carbohydrate binding modules (CBMs) to endoglycosidase activity, and how CBMs work in concert with GH domains to produce optimal activity on IgG.

Novel endo-β-N-acetylglucosaminidases from Tannerella species hydrolyze multibranched complex-type N-glycans with different specificities

Endo-β-N-acetylglucosaminidases are enzymes that hydrolyze the N,N'-diacetylchitobiose unit of N-glycans. Many endo-β-N-acetylglucosaminidases also exhibit transglycosylation activity, which corresponds to the reverse of the hydrolysis reaction. Because of these activities, some of these enzymes have recently been used as powerful tools for glycan remodeling of glycoproteins. Although many endo-β-N-acetylglucosaminidases have been identified and characterized to date, there are few enzymes that exhibit hydrolysis activity toward multibranched (tetra-antennary or more) complex-type N-glycans on glycoproteins. Therefore, we searched for novel endo-β-N-acetylglucosaminidases that exhibit hydrolysis activity toward multibranched complex-type N-glycans in this study. From database searches, we selected three candidate enzymes from Tannerella species-Endo-Tsp1006, Endo-Tsp1263 and Endo-Tsp1457-and prepared them as recombinant proteins. We analyzed the hydrolysis activity of these enzymes toward N-glycans on glycoproteins and found that Endo-Tsp1006 and Endo-Tsp1263 exhibited hydrolysis activity toward complex-type N-glycans, including multibranched N-glycans, preferentially, whereas Endo-Tsp1457 exhibited hydrolysis activity toward high-mannose-type N-glycans exclusively. We further analyzed substrate specificities of Endo-Tsp1006 and Endo-Tsp1263 using 18 defined glycopeptides as substrates, each having a different N-glycan structure. We found that Endo-Tsp1006 preferred N-glycans with galactose or α2,6-linked sialic acid residues in their nonreducing ends as substrates, whereas Endo-Tsp1263 preferred N-glycans with N-acetylglucosamine residues in their nonreducing ends as substrates.

Transglycosylation toward naringenin-7-O-glucoside using an N180H mutant of Coprinopsis cinerea endo-β-N-acetylglucosaminidase

Flavonoids are generally glycosylated, and the glycan moieties of flavonoid glycosides are known to greatly affect their physicochemical and biological properties. Thus, the development of a variety of tools for glycan remodeling of flavonoid glycosides is highly desired. An endo-β-N-acetylglucosaminidase mutant Endo-CC N180H, which is developed as an excellent chemoenzymatic tool for creating sialylglycoproteins, was employed for the glycosylation of flavonoids. Endo-CC N180H transferred the sialyl biantennary glycans from the sialylglyco peptide to pNP-GlcNAc and narigenin-7-O-glucoside. The kinetic parameters of Endo-CC N180H towards SGP and pNP-GlcNAc were determined. Flavonoid glucosides harboring a 1,3-diol structure in the glucose moieties acted as substrates of Endo-CC N180H. We proposed that the sialyl biantennary glycan transfer to the flavonoid by Endo-CC N180H could pave the way for the improvement of the inherent biological functions of the flavonoids and creation of novel flavonoid glycoside derivatives for future human health benefits including foods and drugs.

Secretory production of N-glycan-deleted glycoprotein in Aspergillus oryzae

The pharmaceutical industry has a high demand for glycoprotein production. The glycoform of glycoproteins is crucial for pharmacological activity. However, in general, cells produce glycoproteins with a heterologous glycoform, which is unfavorable for making uniform, efficacious therapeutic proteins. Here, to produce more glycoproteins with N-glycan uniformity, we applied the GlycoDelete strategy, in which endo-β-N-acetylglucosaminidase (ENGase) from the fungus Hypocrea jecorina (EndoT) is expressed at the Golgi membrane to cleave N-glycan from secretory glycoproteins, to Aspergillus oryzae cells. First, we selected candidate transmembrane domains to target EndoT to the Golgi membrane in A. oryzae cells, generated constructs for expressing the transmembrane-fused EndoT proteins and produced four potential AoGlycoDelete strains. We then confirmed that these strains produced α-amylase with a molecular weight lower than that of native α-amylase without an effect on growth. To test whether the A. oryzae α-amylase proteins had been cleaved by EndoT, we expressed and purified HA-tagged α-amylase AmyB and glucoamylase GlaA proteins from the AoGlycoDelete strain. MS and N-glycan analyses of the intact proteins confirmed neither AmyB-HA nor GlaA-HA produced from the AoGlycoDelete strain contained N-glycan. Lastly, we determined the enzymatic activities of the amylases produced by the AoGlycoDelete strain, which showed that the lack of N-glycan did not affect their activity under the conditions tested. Collectively, our findings demonstrate successful generation of an AoGlycoDelete strain that might be a good candidate for producing pharmaceutical glycoproteins with a uniform N-glycan structure.

Structural basis for the specific cleavage of core-fucosylated N-glycans by endo-β-N-acetylglucosaminidase from the fungus Cordyceps militaris

N-Linked glycans play important roles in various cellular and immunological events. Endo-β-N-acetylglucosaminidase (ENGase) can release or transglycosylate N-glycans and is a promising tool for the chemoenzymatic synthesis of glycoproteins with homogeneously modified glycans. The ability of ENGases to act on core-fucosylated glycans is a key factor determining their therapeutic utility because mammalian N-glycans are frequently α-1,6-fucosylated. Although the biochemistries and structures of various ENGases have been studied extensively, the structural basis for the recognition of the core fucose and the asparagine-linked GlcNAc is unclear. Herein, we determined the crystal structures of a core fucose-specific ENGase from the caterpillar fungus Cordyceps militaris (Endo-CoM), which belongs to glycoside hydrolase family 18. Structures complexed with fucose-containing ligands were determined at 1.75-2.35 Å resolutions. The fucose moiety linked to GlcNAc is extensively recognized by protein residues in a round-shaped pocket, whereas the asparagine moiety linked to the GlcNAc is exposed to the solvent. The N-glycan-binding cleft of Endo-CoM is Y-shaped, and several lysine and arginine residues are present at its terminal regions. These structural features were consistent with the activity of Endo-CoM on fucose-containing glycans on rituximab (IgG) and its preference for a sialobiantennary substrate. Comparisons with other ENGases provided structural insights into their core fucose tolerance and specificity. In particular, Endo-F3, a known core fucose-specific ENGase, has a similar fucose-binding pocket, but the surrounding residues are not shared with Endo-CoM. Our study provides a foothold for protein engineering to develop enzymatic tools for the preparation of more effective therapeutic antibodies.

Fluorogenic probe for measuring high-mannose type glycan-specific endo-β-N-acetylglucosaminidase H activity

We synthesized a fluorogenic probe with a high-mannose type heptasaccharide structure to detect the hydrolytic activity of endo-β-N-acetylglucosaminidase from Streptomyces plicatus (Endo-H). The heptasaccharide derivative (1) was labeled with an N-methylanthraniloyl group as a reporter dye at the branching point of the β-mannoside residue and 2,4-dinitrophenyl group as a quencher molecule at the reducing end, which was hydrolyzed by Endo-H, resulting in increased fluorescence intensity. Thus, Endo-H activities could be evaluated easily and quantitatively by measuring the fluorescence signal. Using both this probe (1) and a previously synthesized pentasaccharide probe, the hydrolysis activity of Endo-H and Endo-M were investigated. The results clearly showed a correlation with the substrate specificity of each enzyme.

Chemoenzymatic Methods for the Synthesis of Glycoproteins

Glycosylation is one of the most prevalent posttranslational modifications that profoundly affects the structure and functions of proteins in a wide variety of biological recognition events. However, the structural complexity and heterogeneity of glycoproteins, usually resulting from the variations of glycan components and/or the sites of glycosylation, often complicates detailed structure-function relationship studies and hampers the therapeutic applications of glycoproteins. To address these challenges, various chemical and biological strategies have been developed for producing glycan-defined homogeneous glycoproteins. This review highlights recent advances in the development of chemoenzymatic methods for synthesizing homogeneous glycoproteins, including the generation of various glycosynthases for synthetic purposes, endoglycosidase-catalyzed glycoprotein synthesis and glycan remodeling, and direct enzymatic glycosylation of polypeptides and proteins. The scope, limitation, and future directions of each method are discussed.

Acceptor range of endo-β-N-acetylglucosaminidase mutant endo-CC N180H: from monosaccharide to antibody

The endo-β-N-acetylglucosaminidase mutant endo-CC N180H transfers glycan from sialylglycopeptide (SGP) to various acceptors. The scope and limitations of low-molecular-weight acceptors were investigated. Several homogeneous glycan-containing compounds, especially those with potentially useful labels or functional moieties, and possible reagents in glycoscience were synthesized. The 1,3-diol structure is important in acceptor molecules in glycan transfer reactions mediated by endo-CC N180H as well as by endo-M-N175Q. Glycan remodelling of antibodies was explored using core-fucose-deficient anti-CCR4 antibody with SGP and endo-CC N180H. Homogeneity of the glycan in the antibody was confirmed by mass spectrometry without glycan cleavage.

The ENGases: versatile biocatalysts for the production of homogeneous N-linked glycopeptides and glycoproteins

The endo-β-N-acetylglucosaminidases (ENGases) are an enzyme class (EC 3.2.1.96) produced by a range of organisms, ranging from bacteria, through fungi, to higher order species, including humans, comprising two-sub families of glycosidases which all cleave the chitobiose core of N-linked glycans. Synthetic applications of these enzymes, i.e. to catalyse the reverse of their natural hydrolytic mode of action, allow the attachment of N-glycans to a wide variety of substrates which contain an N-acetylglucosamine (GlcNAc) residue to act as an 'acceptor' handle. The use of N-glycan oxazolines, high energy intermediates on the hydrolytic pathway, as activated donors allows their high yielding attachment to almost any amino acid, peptide or protein that contains a GlcNAc residue as an acceptor. The synthetic effectiveness of these biocatalysts has been significantly increased by the production of mutant glycosynthases; enzymes which can still catalyse synthetic processes using oxazolines as donors, but which do not hydrolyse the reaction products. ENGase biocatalysts are now finding burgeoning application for the production of biologically active glycopeptides and glycoproteins, including therapeutic monoclonal antibodies (mAbs) for which the oligosaccharides have been remodelled to optimise effector functions.

Draft Genome Sequence of Sphingobacterium sp. Strain HMA12, Which Encodes Endo-β-N-Acetylglucosaminidases and Can Specifically Hydrolyze Fucose-Containing Oligosaccharides

The genome sequence of the soil bacterium Sphingobacterium sp. strain HMA12, the culture supernatant of which exhibited endo-β-N-acetylglucosaminidase (ENGase) activity, was examined for ENGase-encoding genes. Here, we report the characterization of new genes of ENGases, obtained by whole-genome shotgun sequencing, that are capable of specifically hydrolyzing fucose-containing oligosaccharides.

Characterization of novel endo-β-N-acetylglucosaminidases from Sphingobacterium species, Beauveria bassiana and Cordyceps militaris that specifically hydrolyze fucose-containing oligosaccharides and human IgG

Endo-β-N-acetylglucosaminidase (ENGase) catalyzes hydrolysis of N-linked oligosaccharides. Although many ENGases have been characterized from various organisms, so far no fucose-containing oligosaccharides-specific ENGase has been identified in any organism. Here, we screened soil samples, using dansyl chloride (Dns)-labeled sialylglycan (Dns-SG) as a substrate, and discovered a strain that exhibits ENGase activity in the culture supernatant; this strain, named here as strain HMA12, was identified as a Sphingobacterium species by 16S ribosomal RNA gene analysis. By draft genome sequencing, five candidate ENGase encoding genes were identified in the genome of this strain. Among them, a recombinant protein purified from Escherichia coli expressing the candidate gene ORF1188 exhibited fucose-containing oligosaccharides-specific ENGase activity. The ENGase exhibited optimum activities at very acidic pHs (between pH 2.3–2.5). A BLAST search using the sequence of ORF1188 identified two fungal homologs, one in Beauveria bassiana and the other in Cordyceps militaris. Recombinant ORF1188, Beauveria and Cordyceps ENGases released the fucose-containing oligosaccharides residues from rituximab (immunoglobulin G) but not the high-mannose-containing oligosaccharides residues from RNase B, a result that not only confirmed the substrate specificity of these novel ENGases but also suggested that natural glycoproteins could be their substrates.

Preparation and biological activities of anti-HER2 monoclonal antibodies with fully core-fucosylated homogeneous bi-antennary complex-type glycans

Recently, the absence of a core-fucose residue in the N-glycan has been implicated to be important for enhancing antibody-dependent cellular cytotoxicity (ADCC) activity of immunoglobulin G monoclonal antibodies (mAbs). Here, we first prepared anti-HER2 mAbs having two core-fucosylated N-glycan chains with the single G2F, G1aF, G1bF, or G0F structure, together with those having two N-glycan chains with a single non-core-fucosylated corresponding structure for comparison, and determined their biological activities. Dissociation constants of mAbs with core-fucosylated N-glycans bound to recombinant Fcγ-receptor type IIIa variant were 10 times higher than those with the non-core-fucosylated N-glycans, regardless of core glycan structures. mAbs with the core-fucosylated N-glycans had markedly reduced ADCC activities, while those with the non-core-fucosylated N-glycans had high activities. These results indicate that the presence of a core-fucose residue in the N-glycan suppresses the binding to the Fc-receptor and the induction of ADCC of anti-HER2 mAbs.

Structural modeling and mutagenesis of endo-β-N-acetylglucosaminidase from Ogataea minuta identifies the importance of Trp295 for hydrolytic activity

Endo-β-N-acetylglucosaminidase from the methylotrophic yeast Ogataea minuta (Endo-Om) is a glycoside hydrolase family 85 enzyme that has dual catalytic activity in the hydrolysis and transglycosylation of complex N-glycans, in common with the enzymes from the eukaryotic species. In this study, we have conducted mutagenesis of Endo-Om at Trp295, to determine the effect on hydrolytic activity. Structural modeling predicted that Trp295 forms an important interaction with the α-1,3-linked mannose residue of the trimannosyl N-glycan core, rather than being directly involved in catalytic activity. Our results showed that an aromatic amino acid is required at position 295 for the hydrolytic activity of this enzyme. Notably, the tryptophan residue is highly conserved in eukaryotic endo-β-N-acetylglucosaminidases that show activity toward complex oligosaccharides. Accordingly, our results strongly suggested that Trp295 is involved in the recognition of oligosaccharide substrates by Endo-Om.

Synthesis of Glycosides by Glycosynthases

The many advances in glycoscience have more and more brought to light the crucial role of glycosides and glycoconjugates in biological processes. Their major influence on the functionality and stability of peptides, cell recognition, health and immunity and many other processes throughout biology has increased the demand for simple synthetic methods allowing the defined syntheses of target glycosides. Additional interest in glycoside synthesis has arisen with the prospect of producing sustainable materials from these abundant polymers. Enzymatic synthesis has proven itself to be a promising alternative to the laborious chemical synthesis of glycosides by avoiding the necessity of numerous protecting group strategies. Among the biocatalytic strategies, glycosynthases, genetically engineered glycosidases void of hydrolytic activity, have gained much interest in recent years, enabling not only the selective synthesis of small glycosides and glycoconjugates, but also the production of highly functionalized polysaccharides. This review provides a detailed overview over the glycosylation possibilities of the variety of glycosynthases produced until now, focusing on the transfer of the most common glucosyl-, galactosyl-, xylosyl-, mannosyl-, fucosyl-residues and of whole glycan blocks by the different glycosynthase enzyme variants.

Highly efficient transglycosylation of sialo-complex-type oligosaccharide using Coprinopsis cinerea endoglycosidase and sugar oxazoline

OBJECTIVES

To establish an efficient method of chemoenzymatic modification for making N-linked oligosaccharide chains of glycoproteins structurally homogeneous, which crucially affects their bioactivities.

RESULTS

Deglycosylated-RNase B (GlcNAc-RNase B; acceptor), sialylglyco (SG)-oxazoline (donor) and an N180H mutant of Coprinopsis cinerea endo-β-N-acetylglucosaminidase (Endo-CC^N180H) were employed. pH 7.5 was ideal for both SG-oxazoline's stability and Endo-CC's transglycosylation reaction. The most efficient reaction conditions for producing glycosylated-RNase B, virtually modified completely with sialo-biantennary-type complex oligosaccharide, were: 80 μg GlcNAc-RNase B, 200 μg SG-oxazoline and 3 μg Endo-CC^N180H in 20 μl 20 mM Tris/HCl pH 7.5 at 30 °C for 30-60 min.

CONCLUSIONS

This transglycosylation method using SG-oxazoline and Endo-CC^N180H is beneficial for producing pharmaceutical glycoproteins modified with homogenous biantennary-complex-type oligosaccharides.

Generation of a Mutant Mucor hiemalis Endoglycosidase That Acts on Core-fucosylated N-Glycans

Endo-β-N-acetylglucosaminidase M (Endo-M), an endoglycosidase from the fungus Mucor hiemalis, is a useful tool for chemoenzymatic synthesis of glycoconjugates, including glycoprotein-based therapeutics having a precisely defined glycoform, by virtue of its transglycosylation activity. Although Endo-M has been known to act on various N-glycans, it does not act on core-fucosylated N-glycans, which exist widely in mammalian glycoproteins, thus limiting its application. Therefore, we performed site-directed mutagenesis on Endo-M to isolate mutant enzymes that are able to act on mammalian-type core-α1,6-fucosylated glycans. Among the Endo-M mutant enzymes generated, those in which the tryptophan at position 251 was substituted with alanine or asparagine showed altered substrate specificities. Such mutant enzymes exhibited increased hydrolysis of a synthetic α1,6-fucosylated trimannosyl core structure, whereas their activity on the afucosylated form decreased. In addition, among the Trp-251 mutants, the W251N mutant was most efficient in hydrolyzing the core-fucosylated substrate. W251N mutants could act on the immunoglobulin G-derived core-fucosylated glycopeptides and human lactoferrin glycoproteins. This mutant was also capable of transferring the sialyl glycan from an activated substrate intermediate (sialyl glyco-oxazoline) onto an α1,6-fucosyl-N-acetylglucosaminyl biotin. Furthermore, the W251N mutant gained a glycosynthase-like activity when a N175Q substitution was introduced and it caused accumulation of the transglycosylation products. These findings not only give insights into the substrate recognition mechanism of glycoside hydrolase family 85 enzymes but also widen their scope of application in preparing homogeneous glycoforms of core-fucosylated glycoproteins for the production of potent glycoprotein-based therapeutics.

Advances in Enzymatic Glycoside Synthesis

A robust platform for facile defined glycan synthesis does not exist. Yet the need for such technology has never been greater as researchers seek to understand the full scope of carbohydrate function, stretching beyond the classical roles of structure and energy storage to encompass highly nuanced cell signaling events. To comprehensively explore and exploit the full diversity of carbohydrate functions, we must first be able to synthesize them in a controlled manner. Toward this goal, traditional chemical syntheses are inefficient while nature's own synthetic enzymes, the glycosyl transferases, can be challenging to express and expensive to employ on scale. Glycoside hydrolases represent a pool of glycan processing enzymes that can be either used in a transglycosylation mode or, better, engineered to function as "glycosynthases," mutant enzymes capable of assembling glycosides. Glycosynthases grant access to valuable glycans that act as functional and structural probes or indeed as inhibitors and therapeutics in their own right. The remodelling of glycosylation patterns in therapeutic proteins via glycoside hydrolases and their mutants is an exciting frontier in both basic research and industrial scale processes.