GH18 endo-β-N-acetylglucosaminidases use distinct mechanisms to process hybrid-type N-linked glycans

Glycosylation in cancer: mechanisms, diagnostic markers, and therapeutic applications

Glycosylation, a key post-translational modification, plays a pivotal role in cancer progression by influencing critical processes such as protein folding, immune modulation, and intercellular signaling. Altered glycosylation patterns are increasingly recognized as fundamental drivers of tumorigenesis, contributing to key cancer hallmarks like enhanced tumor migration, metastasis, and immune evasion. These aberrant glycosylation signatures not only offer insights into cancer biology but also serve as valuable diagnostic markers and potential therapeutic targets across a range of malignancies. This review explores the mechanisms underlying glycosylation alterations in cancer. We discuss the molecular basis of these changes, including genetic mutations, epigenetic regulation, and oncogene-driven shifts in glycosylation pathways. Additionally, we highlight recent advancements in glycomics research, with a focus on how these alterations influence tumor progression, angiogenesis, and the tumor microenvironment. Furthermore, the review considers the clinical implications of glycosylation changes, including their role in resistance to anti-cancer therapies and their potential as biomarkers for personalized treatment strategies. By bridging fundamental glycosylation research with clinical applications, this review underscores the promise of glycosylation as both a diagnostic tool and a therapeutic target in oncology, offering new avenues for improved patient stratification and precision medicine.

Characterization and application in recombinant N-GlcNAc-protein production of a novel endo-β-N-acetylglucosaminidase from Listeria booriae

Endo-β-N-acetylglucosaminidases (ENGases) are essential enzymes for hydrolyzing N-glycans, with applications in protein N-glycosylation analysis and glycoprotein synthesis. In this study, a novel GH18 family ENGase, Endo-LB, was identified from Listeria booriae FSL A5-0281. Composed of 593 amino acids (65.78 kDa), Endo-LB features with two domains: an Endo S-like catalytic domain and a mucin-binding protein (MucBP) domain. Recombinant Endo-LB, expressed in Escherichia coli BL21 (DE3) pLysS, exhibited a specific activity of 198.25 U/mg and hydrolyzed high mannose-type N-glycans at a temperature from 4 °C to 60 °C with optimal activity at 37 °C and pH 6.0 (range 3.0 to 10.0), making it versatile for various environmental conditions. The MucBP domain does not affect soluble Endo-LB activity but influences interaction with mucin on cell surface, suggesting potential application in targeting specific glycoproteins in complex biological environments. To address the heterogeneity of N-glycans in Pichia pastoris (Komagataella phaffii) expression, Endo-LB was further expressed in the Golgi of P. pastoris, efficiently producing glycoproteins, such as Erythropoietin (EPO) (37 mg/L) and Darbepoetin α (53 mg/L) with nearly complete N-glycans truncation, which can be further extended to generate diverse N-glycan structures. These findings highlight the versatility and potential utility of Endo-LB in glycoprotein engineering and biotechnological applications.

Human gut microbes express functionally distinct endoglycosidases to metabolize the same N-glycan substrate

Bacteroidales (syn. Bacteroidetes) are prominent members of the human gastrointestinal ecosystem mainly due to their efficient glycan-degrading machinery, organized into gene clusters known as polysaccharide utilization loci (PULs). A single PUL was reported for catabolism of high-mannose (HM) N-glycan glyco-polypeptides in the gut symbiont Bacteroides thetaiotaomicron, encoding a surface endo-β-N-acetylglucosaminidase (ENGase), BT3987. Here, we discover an ENGase from the GH18 family in B. thetaiotaomicron, BT1285, encoded in a distinct PUL with its own repertoire of proteins for catabolism of the same HM N-glycan substrate as that of BT3987. We employ X-ray crystallography, electron microscopy, mass spectrometry-based activity measurements, alanine scanning mutagenesis and a broad range of biophysical methods to comprehensively define the molecular mechanism by which BT1285 recognizes and hydrolyzes HM N-glycans, revealing that the stabilities and activities of BT1285 and BT3987 were optimal in markedly different conditions. BT1285 exhibits significantly higher affinity and faster hydrolysis of poorly accessible HM N-glycans than does BT3987. We also find that two HM-processing endoglycosidases from the human gut-resident Alistipes finegoldii display condition-specific functional properties. Altogether, our data suggest that human gut microbes employ evolutionary strategies to express distinct ENGases in order to optimally metabolize the same N-glycan substrate in the gastroinstestinal tract.

Modulating antibody effector functions by Fc glycoengineering

Antibody based drugs, including IgG monoclonal antibodies, are an expanding class of therapeutics widely employed to treat cancer, autoimmune and infectious diseases. IgG antibodies have a conserved N-glycosylation site at Asn297 that bears complex type N-glycans which, along with other less conserved N- and O-glycosylation sites, fine-tune effector functions, complement activation, and half-life of antibodies. Fucosylation, galactosylation, sialylation, bisection and mannosylation all generate glycoforms that interact in a specific manner with different cellular antibody receptors and are linked to a distinct functional profile. Antibodies, including those employed in clinical settings, are generated with a mixture of glycoforms attached to them, which has an impact on their efficacy, stability and effector functions. It is therefore of great interest to produce antibodies containing only tailored glycoforms with specific effects associated with them. To this end, several antibody engineering strategies have been developed, including the usage of engineered mammalian cell lines, in vitro and in vivo glycoengineering.

N-glycan breakdown by bacterial CAZymes

The modification of proteins by N-glycans is ubiquitous to most organisms and they have multiple biological functions, including protecting the adjoining protein from degradation and facilitating communication or adhesion between cells, for example. Microbes have evolved CAZymes to deconstruct different types of N-glycans and some of these have been characterised from microbes originating from different niches, both commensals and pathogens. The specificity of these CAZymes provides clues as to how different microbes breakdown these substrates and possibly cross-feed them. Discovery of CAZymes highly specific for N-glycans also provides new tools and options for modifying glycoproteins.

Mechanism of antibody-specific deglycosylation and immune evasion by Streptococcal IgG-specific endoglycosidases

Bacterial pathogens have evolved intricate mechanisms to evade the human immune system, including the production of immunomodulatory enzymes. Streptococcus pyogenes serotypes secrete two multi-modular endo-β-N-acetylglucosaminidases, EndoS and EndoS2, that specifically deglycosylate the conserved N-glycan at Asn297 on IgG Fc, disabling antibody-mediated effector functions. Amongst thousands of known carbohydrate-active enzymes, EndoS and EndoS2 represent just a handful of enzymes that are specific to the protein portion of the glycoprotein substrate, not just the glycan component. Here, we present the cryoEM structure of EndoS in complex with the IgG1 Fc fragment. In combination with small-angle X-ray scattering, alanine scanning mutagenesis, hydrolytic activity measurements, enzyme kinetics, nuclear magnetic resonance and molecular dynamics analyses, we establish the mechanisms of recognition and specific deglycosylation of IgG antibodies by EndoS and EndoS2. Our results provide a rational basis from which to engineer novel enzymes with antibody and glycan selectivity for clinical and biotechnological applications.

Mass Spectrometry-Based Methods to Determine the Substrate Specificities and Kinetics of N-Linked Glycan Hydrolysis by Endo-β-N-Acetylglucosaminidases

Glycosylation is a common posttranslational modification of proteins and refers to the covalent addition of glycans, chains of polysaccharides, onto proteins producing glycoproteins. The glycans influence the structure, function, and stability of proteins. They also play an integral role in the immune system, and aberrantly glycosylated proteins have wide ranging effects, including leading to diseases such as autoimmune conditions and cancer. Carbohydrate-active enzymes (CAZymes) are produced in bacteria, fungi, and humans and are enzymes which modify glycans via the addition or subtraction of individual or multiple saccharides from glycans. One of the hurdles in studying these enzymes is determining the types of substrates each enzyme is specific for and the kinetics of enzymatic activity. In this chapter, we discuss methods which are currently used to study the substrate specificity and kinetics of CAZymes and introduce a novel mass spectrometry-based technique which enables the specificity and kinetics of CAZymes to be determined accurately and efficiently.

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.

Sculpting therapeutic monoclonal antibody N-glycans using endoglycosidases

Immunoglobulin G (IgG) monoclonal antibodies are a prominent and expanding class of therapeutics used for the treatment of diverse human disorders. The chemical composition of the N-glycan on the fragment crystallizable (Fc) region determines the effector functions through interaction with the Fc gamma receptors and complement proteins. The chemoenzymatic synthesis using endo-β-N-acetylglucosaminidases (ENGases) emerged as a strategy to obtain antibodies with customized glycoforms that modulate their therapeutic activity. We discuss the molecular mechanism by which ENGases recognize different N-glycans and protein substrates, especially those that are specific for IgG antibodies, in order to rationalize the glycoengineering of immunotherapeutic antibodies, which increase the impact on the treatment of myriad diseases.