FcγR-binding affinity of monoclonal murine IgG1s carrying different N-linked Fc oligosaccharides

Selective bioorthogonal probe for N-glycan hybrid structures

Metabolic incorporation of chemically tagged monosaccharides is a facile means of tagging cellular glycoproteins and glycolipids. However, since the monosaccharide precursors are often shared by several pathways, selectivity has been difficult to attain. For example, N-linked glycosylation is a chemically complex and ubiquitous posttranslational modification, with three distinct classes of GlcNAc-containing N-glycan structures: oligomannose, hybrid and complex. Here we describe the synthesis of 1,3-Pr2-6-OTs GlcNAlk (MM-JH-1) as a next-generation metabolic chemical reporter for the selective labeling of hybrid N-glycan structures. We first developed a general strategy for defining the selectivity of labeling with chemically tagged monosaccharides. We then applied this approach to establish that MM-JH-1 is selectively incorporated into hybrid N-glycans. Using this metabolic chemical reporter as a detection tool, we performed imaging and fractionation to define features of the intracellular localization and trafficking of target proteins bearing hybrid N-glycan structures.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Relative quantitation of glycans in cetuximab using ultra-high-performance liquid chromatography-high-resolution mass spectrometry by Pronase E digestion

Glycans play important roles in the activity and function of monoclonal antibodies (mAbs). In this study, an isotope labeling method for the relative quantitative analysis of glycans in cetuximab, a chimeric human/mouse IgG1 monoclonal antibody that specifically targets epidermal growth factor receptor, via hydrophilic interaction LC-ultra-high-performance LC-HRMS was established based on Pronase E digestion. To this aim, novel isotope MS probes, i.e., 3-benzoyl-2-oxothiazolidine-4-carboxylic acid (d0-BOTC) and 3-(2,3,4,5,6-pentadeuterio-benzoyl)-2-oxothiazolidine-4-carboxylate acid (d5-BOTC), which include a carboxyl group to target the amino functional group in glycosylamine, were developed. The nonspecific Pronase E enzyme could simultaneously digest the peptide bound to the N- and O-glycans into glycosylamine having only one amino acid. Since the mass difference between the light- and heavy-labeled glycans was 5.0 Da, the relative abundance of their MS peaks was used to achieve the qualitative and relative quantitative analysis of glycans. Sialylglycopeptide was used as a complex glycan model to validate the accuracy of the method. The results demonstrated the good linearity (R² ≥ 0.9994) between the experimentally detected MS intensity ratios and the theoretical molar ratios of the d0-BOTC to the corresponding d5-BOTC derivatives in the dynamic range of 0.03-10 and 0.03-20 of three orders magnitude for the d5-BOTC/d0-BOTC ratios. The reproducibility was between 0.16% and 10.70%, and the limit of detection was 13 fmol. The feasibility of the relative quantification method was investigated by analyzing the glycan content in cetuximab, finding good consistency between experimental and theoretical molar ratios (5:1, 3:1, 1:1, 1:3, 1:5) of d0/d5-BOTC-labeled glycans. Finally, 13 glycans were successfully identified in cetuximab by applying this method using an in-house Tracefinder database. This study provides a novel strategy for the high throughput analysis, identification, and functional study of glycans in mAbs.

Cell engineering for the production of hybrid-type N-glycans in HEK293 cells

Glycoprotein therapeutics are among the leading products in the biopharmaceutical industry. The heterogeneity of glycans in therapeutic proteins is an issue for maintaining quality, activity, and safety during bioprocessing. In this study, we knocked out genes encoding Golgi α-mannosidase-II, MAN2A1 and MAN2A2 in human embryonic kidney 293 (HEK293) cells, establishing an M2D-KO cell line that can produce recombinant proteins mainly with hybrid-type N-glycans. Furthermore, FUT8, which encodes α1,6-fucosyltransferase, was knocked out in the M2D-KO cell line, establishing a DF-KO cell line that can express non-core fucosylated hybrid-type N-glycans. Two recombinant proteins, lysosomal acid lipase (LIPA) and constant fragment (Fc) of human IgG1, were expressed in the M2D-KO and DF-KO cell lines. Glycan structural analysis revealed that complex-type N-glycans were removed in both M2D-KO and DF-KO cells. Our results suggest that these cell lines are suitable for the production of therapeutic proteins with hybrid-type N-glycans. Moreover, KO cell lines would be useful as models for researching the mechanism of antimetastatic effects in human tumors by swainsonine treatment.

Immunoglobulin G Glycosylation Changes in Aging and Other Inflammatory Conditions

Among the multiple roles played by protein glycosylation, the fine regulation of biological interactions is one of the most important. The asparagine 297 (Asn₂₉₇) of IgG heavy chains is decorated by a diantennary glycan bearing a number of galactose and sialic acid residues on the branches ranging from 0 to 2. In addition, the structure can present core-linked fucose and/or a bisecting GlcNAc. In many inflammatory and autoimmune conditions, as well as in metabolic, cardiovascular, infectious, and neoplastic diseases, the IgG Asn₂₉₇-linked glycan becomes less sialylated and less galactosylated, leading to increased expression of glycans terminating with GlcNAc. These conditions alter also the presence of core-fucose and bisecting GlcNAc. Importantly, similar glycomic alterations are observed in aging. The common condition, shared by the above-mentioned pathological conditions and aging, is a low-grade, chronic, asymptomatic inflammatory state which, in the case of aging, is known as inflammaging. Glycomic alterations associated with inflammatory diseases often precede disease onset and follow remission. The aberrantly glycosylated IgG glycans associated with inflammation and aging can sustain inflammation through different mechanisms, fueling a vicious loop. These include complement activation, Fcγ receptor binding, binding to lectin receptors on antigen-presenting cells, and autoantibody reactivity. The complex molecular bases of the glycomic changes associated with inflammation and aging are still poorly understood.