Quantitative Analysis of Therapeutic Antibody Interactions with Fcγ Receptors Using High-Speed Atomic Force Microscopy.

This study employed high-speed atomic force microscopy to quantitatively analyze the interactions between therapeutic antibodies and Fcγ receptors (FcγRs). Antibodies are essential components of the immune system and are integral to biopharmaceuticals. The focus of this study was on immunoglobulin G molecules, which are crucial for antigen binding via the Fab segments and cytotoxic functions through their Fc portions. We conducted real-time, label-free observations of the interactions of rituximab and mogamulizumab with the recombinant FcγRIIIa and FcγRIIa. The dwell times of FcγR binding were measured at the single-molecule level, which revealed an extended interaction duration of mogamulizumab with FcγRIIIa compared with that of rituximab. This is linked to enhanced antibody-dependent cellular cytotoxicity that is attributed to the absence of the core fucosylation of Fc-linked N-glycan. This study also emphasizes the crucial role of the Fab segments in the interaction with FcγRIIa as well as that with FcγRIIIa. This approach provided quantitative insight into therapeutic antibody interactions and exemplified kinetic proofreading, where cellular discrimination relies on ligand residence times. Observing the dwell times of antibodies on the effector molecules has emerged as a robust indicator of therapeutic antibody efficacy. Ultimately, these findings pave the way for the development of refined therapeutic antibodies with tailored interactions with specific FcγRs. This research contributes to the advancement of biopharmaceutical antibody design and optimizing antibody-based treatments for enhanced efficacy and precision.

N-glycan structures of human alveoli provide insight into influenza A virus infection and pathogenesis.

The rapidly evolvable influenza A virus has caused pandemics linked to millions of deaths in the past century. Influenza A viruses are categorized by H (hemagglutinin; HA) and N (neuraminidase; NA) proteins expressed on the viral envelope surface. Analyses of past pandemics suggest that the HA gene segment comes from a nonhuman virus, which is then introduced into an immunologically naïve human population with potentially devastating consequences. As a prerequisite for infection, the nonhuman HA molecules of H1-H16 viruses must be able to bind to specific sialyl receptors on the host cell surface along the human respiratory tract. Thus, additional insight into the structures of host cell glycans and how different HAs interact with different glycans might provide new insight into the mechanisms underlying sustained infection and transmission in humans. In this work, we identified the sialyl N-glycans found in normal human alveoli and characterized the influenza viruses that preferentially bound to these different structures. We also determined the amino acid changes in HA that were linked to a switch of receptor-binding preference from nonhuman to pandemic, as well as pandemic to seasonal. Our data provide insight into why seasonal viruses are associated with reduced alveolar infection and damage and suggest new considerations for designing anti-HA vaccines and drugs. The results provide a better understanding of viral tropism and pathogenesis in humans that will be important for prediction and surveillance of zoonotic, pandemic, and epidemic influenza outbreaks. DATABASE: The novel hemagglutinin nucleotide sequences reported here were deposited in GISAID under the accession numbers of EPI685738 for A/Yamaguchi/20/2006(H1N1) and EPI685740 for A/Kitakyushu/10/2006(H1N1).

N-Glycan Modification of a Recombinant Protein via Coexpression of Human Glycosyltransferases in Silkworm Pupae.

Recombinant proteins produced in insect cells and insects, unlike those produced in mammalian cells, have pauci-mannose-type N-glycans. In this study, we examined complex-type N-glycans on recombinant proteins via coexpression of human ß-1,2-N-acetylglucosaminyltransferase II (hGnT II) and human ß1,4-galactosyltransferase (hGalT I) in silkworm pupae, by using the Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid system. The actin A3 promoter from B. mori and the polyhedrin promoter from Autographa californica multiple nucleopolyhedroviruses (AcMNPVs) were used to coexpress hGnT II and hGalT I. These recombinant BmNPVs were coexpressed with human IgG (hIgG), hGnT II and hGalT I in silkworm pupae. When hIgG was coexpressed with hGnT II, approximately 15% of all N-glycans were biantennary, with both arms terminally modified with N-acetylglucosamine (GlcNAc). In contrast, when hIgG was coexpressed with both hGnT II and hGalT I under the control of the polyhedrin promoter, 27% of all N-glycans were biantennary and terminally modified with GlcNAc, with up to 5% carrying one galactose and 11% carrying two. The obtained N-glycan structure was dependent on the promoters used for coexpression of hGnT II or hGalT I. This is the first report of silkworm pupae producing a biantennary, terminally galactosylated N-glycan in a recombinant protein. These results suggest that silkworms can be used as alternatives to insect and mammalian hosts to produce recombinant glycoproteins with complex N-glycans.

Alteration of a recombinant protein N-glycan structure in silkworms by partial suppression of N-acetylglucosaminidase gene expression.

OBJECTIVE: To synthesize complex type N-glycans in silkworms, shRNAs against the fused lobe from Bombyx mori (BmFDL), which codes N-acetylglucosaminidase (GlcNAcase) in the Golgi, was expressed by recombinant B. mori nucleopolyhedrovirus (BmNPV) in silkworm larvae. RESULTS: Expression was under the control of the actin promoter of B. mori or the U6-2 and i.e.-2 promoters from Orgyia pseudotsugata multiple nucleopolyhedrovirus (OpMNPV). The reduction of specific GlcNAcase activity was observed in Bm5 cells and silkworm larvae using the U6-2 promoter. In silkworm larvae, the partial suppression of BmFDL gene expression was observed. When shRNA against BmFDL was expressed under the control of U6-2 promoter, the Man3GlcNAc(Fuc)GlcNAc structure appeared in a main N-glycans of recombinant human IgG. These results suggested that the control of BmFDL expression by its shRNA in silkworms caused the modification of its N-glycan synthetic pathway, which may lead to the alteration of N-glycans in the expressed recombinant proteins. CONCLUSIONS: Suppression of BmFDL gene expression by shRNA is not sufficient to synthesize complex N-glycans in silkworm larvae but can modify the N-glycan synthetic pathway.

Comparison of analytical methods for profiling N- and O-linked glycans from cultured cell lines : HUPO Human Disease Glycomics/Proteome Initiative multi-institutional study.

The Human Disease Glycomics/Proteome Initiative (HGPI) is an activity in the Human Proteome Organization (HUPO) supported by leading researchers from international institutes and aims at development of disease-related glycomics/glycoproteomics analysis techniques. Since 2004, the initiative has conducted three pilot studies. The first two were N- and O-glycan analyses of purified transferrin and immunoglobulin-G and assessed the most appropriate analytical approach employed at the time. This paper describes the third study, which was conducted to compare different approaches for quantitation of N- and O-linked glycans attached to proteins in crude biological samples. The preliminary analysis on cell pellets resulted in wildly varied glycan profiles, which was probably the consequence of variations in the pre-processing sample preparation methodologies. However, the reproducibility of the data was not improved dramatically in the subsequent analysis on cell lysate fractions prepared in a specified method by one lab. The study demonstrated the difficulty of carrying out a complete analysis of the glycome in crude samples by any single technology and the importance of rigorous optimization of the course of analysis from preprocessing to data interpretation. It suggests that another collaborative study employing the latest technologies in this rapidly evolving field will help to realize the requirements of carrying out the large-scale analysis of glycoproteins in complex cell samples.

Stable isotope labeling of glycoprotein expressed in silkworms using immunoglobulin G as a test molecule.

Silkworms serve as promising bioreactors for the production of recombinant proteins, including glycoproteins and membrane proteins, for structural and functional protein analyses. However, lack of methodology for stable isotope labeling has been a major deterrent to using this expression system for nuclear magnetic resonance (NMR) structural biology. Here we developed a metabolic isotope labeling technique using commercially available silkworm larvae. The fifth instar larvae were infected with baculoviruses for co-expression of recombinant human immunoglobulin G (IgG) as a test molecule, with calnexin as a chaperone. They were subsequently reared on an artificial diet containing (15)N-labeled yeast crude protein extract. We harvested 0.1 mg of IgG from larva with a (15)N-enrichment ratio of approximately 80%. This allowed us to compare NMR spectral data of the Fc fragment cleaved from the silkworm-produced IgG with those of an authentic Fc glycoprotein derived from mammalian cells. Therefore, we successfully demonstrated that our method enables production of isotopically labeled glycoproteins for NMR studies.

NMR-based structural validation of therapeutic antibody produced in Nicotiana benthamiana.

KEY MESSAGE: We successfully developed a method for metabolic isotope labeling of recombinant proteins produced in transgenic tobacco. This enabled assessment of structural integrity of plant-derived therapeutic antibodies by NMR analysis. A variety of expression vehicles have been developed for the production of promising biologics, including plants, fungi, bacteria, insects, and mammals. Glycoprotein biologics often experience altered folding and post-translational modifications that are typified by variant glycosylation patterns. These differences can dramatically affect their efficacy, as exemplified by therapeutic antibodies. However, it is generally difficult to validate the structural integrity of biologics produced using different expression vehicles. To address this issue, we have developed and applied a stable-isotope-assisted nuclear magnetic resonance (NMR) spectroscopy method for the conformational characterization of recombinant antibodies produced in plants. Nicotiana benthamiana used as a vehicle for the production of recombinant immunoglobulin G (IgG) was grown in a (15)N-enriched plant growth medium. The Fc fragment derived from the (15)N-labeled antibody thus prepared was subjected to heteronuclear two-dimensional (2D) NMR measurements. This approach enabled assessment of the structural integrity of the plant-derived therapeutic antibodies by comparing their NMR spectral properties with those of an authentic IgG-Fc derived from mammalian cells.

A structural analysis of N-glycans of neonatal porcine islet-like cell clusters (NPCC).

BACKGROUND: N-glycans isolated from neonatal porcine islet-like cell clusters (NPCCs) were analyzed by a mapping technique, to examine the differences in glycosylation and antigenicity between adult pig islets (APIs) and NPCCs. METHODS: NPCCs were isolated from 1-to-3 day-old neonatal wild-type pigs and cultured for 9 days, using the technique described by Korbutt et al. The extract was proteolyzed by treatment with a chymotrypsin and trypsin mixture and further digested with glycoamidase A to release the N-glycans. After the removal of the peptide materials, the reducing ends of the N-glycans were derivatized with 2-aminopyridine. This mixture was applied to DEAE, amide and ODS columns. PA-oligosaccharides were also subjected to MALDI TOF-MS analysis. RESULTS: The NPCC glycans were comprised of 14 neutral, 5 mono-sialyl and 5 di-sialyl glycans. As a feature of the N-glycans of NPCC, NPCC contained large amounts of high mannose structures. On the other hand, all of the hybrid and complex types contained a Fucα1-6GlcNAc structure, but were not modified with sulfate residues. Among them, the NPCC preparation contained five neutral and two mono-sialyl glycans and two di-sialyl glycans that were not typically found in adult islets, and seven of these nine were not detected in human islets. Moreover, most of the structures could be clearly identified in this study. CONCLUSIONS: The data herein will be helpful for future studies of the glycoantigen associated with NPCC.

A comparison of the main structures of N-glycans of porcine islets with those from humans.

After producing α1-3-galactosyltransferase knockout (GKO) pigs, most of the organs of these pigs showed less antigenicity to the human body. However, wild-type adult pig islets (API) that originally contained negligible levels of α-galactosidase now showed a clear antigenicity to human serum. In this study, N-glycans were isolated from both APIs and human islets. Their structures were then analyzed by a mapping technique based on their high-performance liquid chromatography elution positions and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometric data. Both preparations contained substantial amounts of high-mannose structures. The N-glycans from human islets were separated into 17 neutral, 8 mono-sialyl and 4 di-sialyl glycans, and the API glycans were comprised of 11 neutral, 8 mono-sialyl, 3 di-sialyl, 2 mono-sulfated, 3 mono-sialyl-mono-sulfated and 1 di-sulfated glycans. Among them, the API preparation contained one neutral, five mono-sialyl glycans and six sulfated glycans that were not detected in human islets. The structures of 9 of these 12 could be clearly determined. In addition, a study of the sulfate-depleted API suggests that sulfate residues could be antigenic to humans. The data herein will be helpful for future studies of the antigenicity associated with API.

Sialic acid cyclization of human Th homing receptor glycan associated with recurrent exacerbations of atopic dermatitis.

BACKGROUND: The molecular pathogenesis underlying recurrent exacerbations of atopic dermatitis (AD) is unclear. Some peripheral CCR4(+) and CCR7(+) helper memory T cells express the specific homing receptor, sialyl 6-sulfo Lewis X (G152 glycan). This glycan loses receptor activity via cyclization of its sialic acid moiety, thus becoming cyclic sialyl 6-sulfo Lewis X (G159 glycan). These findings suggest that the disordered expression of G152 and G159 glycans may be associated with recurrent exacerbations of AD. OBJECTIVE: To assess the possible association of G152 and G159 glycans, which are expressed on peripheral helper T (Th) cells, with frequency of exacerbations. METHODS: The percentage of glycan-expressing cells among peripheral blood CD4(+)CD45RO(+) lymphocytes was determined by flow cytometry. The association of glycans with the frequency of exacerbations determined by recurrence scores as well as with current disease activity was statistically tested. RESULTS: Current disease activity was significantly associated with CCR4(+)CCR7(-) memory Th cells expressing CSLEX-1 glycan, the conventional skin-trafficking receptor without sialic-acid-cyclization activity. In contrast, the frequency of exacerbations was positively and negatively associated with CCR4(+)CCR7(+) memory Th cells expressing G152 and G159 glycans, respectively. Receiver operating characteristics analyses indicated that the ratio of the G152(+)/G159(+) cell percentages discriminated patients with highly recurrent AD with the best accuracy. CONCLUSION: Flow cytometric determination of G159 and G152 glycans on peripheral helper memory T cells may be clinically useful for identifying patients with highly recurrent AD. Disordered sialic acid cyclization of G152 glycan may underlie highly recurrent AD, which may provide a novel therapeutic approach.

N-glycans from porcine trachea and lung: predominant NeuAcα2-6Gal could be a selective pressure for influenza variants in favor of human-type receptor.

It is known that pigs acted as "mixing vessels" for genesis of a new reassortant influenza strain responsible for pandemic H1N1 2009. However, the host factors driving the evolution of a reassorted virus in pigs to 'jump species' resulting in a human outbreak remain unclear. N-glycans derived from the porcine respiratory tract were enzymatically released, fluorescent labeled with 2-aminopyridine, separated according to charge, size and hydrophobicity, and structurally identified by a two-dimensional (size and hydrophobicity) HPLC mapping technique and MALDI-TOF mass spectrometry before and after exo-glycosidase digestion. We found a 3-, 5-, and 13-fold increases in NeuAcα2-6, a preferable human influenza receptor, over NeuAcα2-3, an avian influenza receptor, from upper and lower parts of the porcine trachea towards the porcine lung, a major target organ for swine virus replication. The large proportion of NeuAcα2-6 may exert selective pressure for selection of influenza variants with altered receptor preference for this human-type α2-6 receptor, a crucial first step for generating a human pandemic.

Development and Application of Multidimensional HPLC Mapping Method for O-linked Oligosaccharides.

Glycosylation improves the solubility and stability of proteins, contributes to the structural integrity of protein functional sites, and mediates biomolecular recognition events involved in cell-cell communications and viral infections. The first step toward understanding the molecular mechanisms underlying these carbohydrate functionalities is a detailed characterization of glycan structures. Recently developed glycomic approaches have enabled comprehensive analyses of N-glycosylation profiles in a quantitative manner. However, there are only a few reports describing detailed O-glycosylation profiles primarily because of the lack of a widespread standard method to identify O-glycan structures. Here, we developed an HPLC mapping method for detailed identification of O-glycans including neutral, sialylated, and sulfated oligosaccharides. Furthermore, using this method, we were able to quantitatively identify isomeric products from an in vitro reaction catalyzed by N-acetylglucosamine-6O-sulfotransferases and obtain O-glycosylation profiles of serum IgA as a model glycoprotein.

Cellular glutathione content modulates the effect of andrographolide on ß-naphthoflavone-induced CYP1A1 mRNA expression in mouse hepatocytes.

We previously reported that andrographolide (Andro), a major bioactive constituent of Andrographis paniculata, synergistically enhanced the inducible expression of CYP1A1 mRNA. In this study, although the synergism was confirmed at 24h after the start of treatment with Andro and ß-naphthoflavone (ßNF), a CYP1A inducer, the expression was profoundly suppressed at an earlier phase, namely at 6-12h, when the ßNF-induced expression peaked. Although oxidized glutathione (GSSG) levels were higher in co-treated cells at 6 and 24h, levels of reactive oxygen species varied depending on the treatment period and species, indicating no relation to the synergistic expression of CYP1A1 mRNA. Glutathione (GSH) and N-acetyl-l-cysteine (NAC) significantly enhanced the ßNF-induced expression, and partly reversed the suppressive effect of Andro in the early phase. At 24h, the addition of GSH or NAC had no effect on ßNF-induced CYP1A1 mRNA expression, but significantly reduced the synergistic effect of Andro. The synergistic effect was enhanced by l-buthionine-(S,R)-sulfoximine, a GSH depleter. Furthermore, H(2)O(2) and ascorbic acid further modified the profile of synergism of Andro on ßNF-inducible CYP1A1 mRNA expression. These results suggest that GSH status might be involved in ßNF-induced CYP1A1 mRNA expression, and the interaction of Andro with GSH might modulate the expression.

Potent modification of inducible CYP1A1 expression by flavonoids.

The present study examined modifications of ß-naphthoflavone (ß-NF)-induced cytochrome P450 1A1 (CYP1A1) expression by flavonoids in mouse hepatocytes in primary culture. Some flavonoids (apigenin, chrysin, flavone, flavanone, galangin, luteolin, and naringenin) by themselves induced CYP1A1 mRNA expression, especially flavone which was even more effective than ß-NF. The effect on ß-NF-induced CYP1A1 mRNA expression was varied, namely additive, suppressive, or both. An additive effect was observed after combined treatment with flavanone, naringenin, and chrysin, whereas kaempferol, myricetin, and quercetin decreased CYP1A1 levels. Apigenin, chrysin, galangin, luteolin, and morin synergistically enhanced ß-NF-induced CYP1A1 expression at 24 h, but considerably suppressed it at 9 h. The structure-activity relationship of flavonoids affecting CYP1A1 expression as inducers or inhibitors is discussed. The present observations suggest the need to reveal the mechanism by which CYP1A1 expression is modified by flavonoids for risk assessment, since CYP1A1 activates environmental carcinogenic polycyclic hydrocarbons and flavonoids are major constituents in food.

Mice deficient in N-acetylgalactosamine 4-sulfate 6-o-sulfotransferase are unable to synthesize chondroitin/dermatan sulfate containing N-acetylgalactosamine 4,6-bissulfate residues and exhibit decreased protease activity in bone marrow-derived mast cells.

Chondroitin sulfate (CS) and dermatan sulfate (DS) containing N-acetylgalactosamine 4,6-bissulfate (GalNAc(4,6-SO(4))) show various physiological activities through interacting with numerous functional proteins. N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of N-acetylgalactosamine 4-sulfate in CS or DS to yield GalNAc(4,6-SO(4)) residues. We here report generation of transgenic mice that lack GalNAc4S-6ST. GalNAc4S-6ST-null mice were born normally and fertile. In GalNAc4S-6ST-null mice, GalNAc(4,6-SO(4)) residues in CS and DS disappeared completely, indicating that GalNAc4S-6ST should be a sole enzyme responsible for the synthesis of GalNAc(4,6-SO(4)) residues in both CS and DS. IdoA-GalNAc(4,6-SO(4)) units that account for approximately 40% of total disaccharide units of DS in the liver of the wild-type mice disappeared in the liver DS of GalNAc4S-6ST-null mice without reduction of IdoA content. Bone marrow-derived mast cells (BMMCs) derived from GalNAc4S-6ST-null mice contained CS without GlcA-GalNAc(4,6-SO(4)) units. Tryptase and carboxypeptidase A activities of BMMCs derived from GalNAc4S-6ST-null mice were lower than those activities of BMMCs derived from wild-type mice, although mRNA expression of these mast cell proteases was not altered. Disaccharide compositions of heparan sulfate/heparin contained in the mast cells derived from BMMCs in the presence of stem cell factor were much different from those of heparan sulfate/heparin in BMMCs but did not differ significantly between wild-type mice and GalNAc4S-6ST-null mice. These observations suggest that CS containing GalNAc(4,6-SO(4)) residues in BMMCs may contribute to retain the active proteases in the granules of BMMCs but not for the maturation of BMMCs into connective tissue-type mast cells.

Gender-associated modulation of inducible CYP1A1 expression by andrographolide in mouse liver.

We previously observed a strong synergistic effect on polycyclic aromatic hydrocarbon (PAH)-induced CYP1A1 expression by andrographolide, a major constituent of an herbal medicine derived from the plant Andrographis paniculata, in mouse hepatocytes in primary culture. The present paper describes confirmation of an enhancing effect of andrographolide on the CYP1 family in vivo in the PAH-responsive C57BL/6 mouse. Andrographolide did not alter CYP1 expression in the PAH-nonresponsive DBA/2 mouse. The enhanced expression induced by andrographolide was observed in male C57BL/6 mice, but not in intact or ovariectomized females, or in orchiectomized male mice. However, treatment with testosterone restored the effect in both orchiectomized males and ovariectomized females. These observations indicate a male hormone-related system to be a crucial mediator of the modulation of CYP1 expression by andrographolide. Precautions should be taken regarding the use of A. paniculata as an alternative medication or health promotion, according to its distinctive characterization on sexually dimorphic modulation of CYP1A1 expression.

Regulatory role of leukocyte-common-antigen-related molecule (LAR) in thymocyte differentiation.

The strength of interaction between the antigenic peptide-loaded MHC (MHC/p) and the TCR determines T-cell fate in the thymus. A high avidity interaction between the TCR and the MHC/p induces apoptosis of self-reactive T cells (negative selection), whereas a moderate avidity interaction rescues thymocytes from apoptosis and permits further differentiation to mature T cells (positive selection). Leukocyte common antigen-related molecule (LAR), a receptor-like protein tyrosine phosphatase, is expressed on immature thymocytes, but its role in thymocyte differentiation has not yet been fully elucidated. We analyzed LAR-deficient mice and demonstrated that LAR deficiency affected the differentiation and expansion of immature thymocytes as well as positive and negative selection. Furthermore, LAR deficiency resulted in a lower Ca2+ response. The results indicate that LAR is an important modulator of TCR signaling that controls thymocyte differentiation.

Alterations in receptor-binding properties of swine influenza viruses of the H1 subtype after isolation in embryonated chicken eggs.

Alterations of the receptor-binding properties of swine influenza A viruses (SIVs) during their isolation in embryonated chicken eggs have not been well studied. In this study, the receptor-binding properties of classical H1 SIVs isolated solely in eggs or Madin-Darby canine kidney (MDCK) cells were examined. Sequencing analysis revealed substitutions of D190V/N or D225G in the haemagglutinin (HA) proteins in egg isolates, whereas MDCK isolates retained HA genes identical to those of the original viruses present in the clinical samples. Egg isolates with substitution of either D190V/N or D225G had increased haemagglutinating activity for mouse and sheep erythrocytes, but reduced activity for rabbit erythrocytes. Additionally, egg isolates with D225G had increased haemagglutination activity for chicken erythrocytes. A direct binding assay using a sialyl glycopolymer that possessed either a 5-N-acetylneuraminic acid (Neu5Ac) alpha2,6galactose (Gal) or a Neu5Acalpha2,3Gal linkage revealed that the egg isolates used in this study showed higher binding activity to the Neu5Acalpha2,3Gal receptor than MDCK isolates. Increased binding activity of the egg isolates to the Neu5Acalpha2,3Gal receptor was also confirmed by haemagglutination assay with resialylated chicken erythrocytes by Galbeta1,3/4GlcNAcalpha2,3-sialyltransferase. These observations were reinforced by flow-cytometric and N-glycan analyses of the erythrocytes. The alpha2,3-linked sialic acids were expressed predominantly on the surface of mouse and sheep erythrocytes. Chicken erythrocytes expressed Neu5Acalpha2,3Gal more abundantly than Neu5Acalpha2,6Gal, and rabbit erythrocytes expressed both 5-N-glycolylneuraminic acid (Neu5Gc) alpha2,6Gal and Neu5Acalpha2,6Gal. Our results demonstrate clearly that classical H1 SIVs undergo alterations in receptor-binding activity associated with an amino acid substitution in the HA protein during isolation and propagation in embryonated chicken eggs.