Cleavage of the terminal N-acetylglucosamine of egg-white ovalbumin N-glycans significantly reduces IgE production and Th2 cytokine secretion

Glycans modulate lipid binding in Lili-Mip lipocalin protein: insights from molecular simulations and protein network analyses

The unique viviparous Pacific Beetle cockroaches provide nutrition to their embryo by secreting milk proteins Lili-Mip, a lipid-binding glycoprotein that crystallises in-vivo. The resolved in-vivo crystal structure of variably glycosylated Lili-Mip shows a classical Lipocalin fold with an eight-stranded antiparallel beta-barrel enclosing a fatty acid. The availability of physiologically unaltered glycoprotein structure makes Lili-Mip a very attractive model system to investigate the role of glycans on protein structure, dynamics, and function. Towards that end, we have employed all-atom molecular dynamics simulations on various glycosylated stages of a bound and free Lili-Mip protein and characterised the impact of glycans and the bound lipid on the dynamics of this glycoconjugate. Our work provides important molecular-level mechanistic insights into the role of glycans in the nutrient storage function of the Lili-Mip protein. Our analyses show that the glycans stabilise spatially proximal residues and regulate the low amplitude opening motions of the residues at the entrance of the binding pocket. Glycans also preserve the native orientation and conformational flexibility of the ligand. However, we find that either deglycosylation or glycosylation with high-mannose and paucimannose on the core glycans, which better mimic the natural insect glycosylation state, significantly affects the conformation and dynamics. A simple but effective distance- and correlation-based network analysis of the protein also reveals the key residues regulating the barrel's architecture and ligand binding characteristics in response to glycosylation.

Loke zupa decoction attenuates bronchial EMT-mediated airway remodelling in chronic asthma through the PI3K-Akt/HIF-1α signaling pathway

CONTEXT

Loke zupa decoction (Lok) is a well-established classic Chinese folk remedy for asthma.

OBJECTIVE

We sought to investigate the effect and mechanism of Lok on asthma airway remodelling and provide novel insights for the prevention and treatment of asthma.

MATERIALS AND METHODS

For in vitro experiments, BEAS-2B cells were assigned into six groups: Control, TGF-β1 (10 μM), TGF-β1 + Lok-20, TGF-β1 + Lok-40, TGF-β1 + Lok-80 μg/mL and TGF-β1 + SB431542 (5 μM). CCK8 and wound healing assays were performed. For in vivo experiments, 60 female BALB/c mice were randomly divided into 5 groups: Control, model, Lok-4.55, Lok-9.1, and DEX group. Lok was administrated by gavage during the challenge stage for 8 consecutive weeks (4.55 and 9.1 g/kg/day). We investigated airway inflammation and airway remodelling in the lungs and verified the activation status of EMT-related markers and the PI3K-Akt/HIF-1α signalling pathway.

RESULTS

In vitro, Lok efficiently inhibited TGF-β1-induced BEAS-2B cell proliferation ability (cell viability 165% vs. 105%) and migration (migration areas 85% vs. 35%) without affecting their normal growth (IC50 274.2 µg/mL at 48 h). In vivo, Lok effectively protected mice from asthma, as evidenced by decreased histological damage and level of cytokines in BALF (IL-4, IL-13 and TGF-β1) by 17%-77%. Mechanistic research revealed that Lok reduced the levels of EMT-related molecules and significantly downregulated the PI3K-Akt/HIF-1α signalling pathway.

DISCUSSION AND CONCLUSIONS

Our findings provide novel insights into the protective effect of Lok on asthma and the underlying mechanisms, providing a theoretical basis and potential treatment possibilities for this patient population.

New Perspectives on Food Matrix Modulation of Food Allergies: Immunomodulation and Component Interactions

Food allergy is a multifactorial interplay process influenced not only by the structure and function of the allergen itself but also by other components of the food matrix. For food, before it is thoroughly digested and absorbed, numerous factors make the food matrix constantly change. This will also lead to changes in the chemistry, biochemical composition, and structure of the various components in the matrix, resulting in multifaceted effects on food allergies. In this review, we reveal the relationship between the food matrix and food allergies and outline the immune role of the components in the food matrix, while highlighting the ways and pathways in which the components in the food matrix interact and their impact on food allergies. The in-depth study of the food matrix will essentially explore the mechanism of food allergies and bring about new ideas and breakthroughs for the prevention and treatment of food allergies.

Epitope mapping and the effects of various factors on the immunoreactivity of main allergens in egg white

Egg white has high protein content and numerous biological/functional properties. However, reported allergenicity for some of the proteins in egg white is an issue that needs to be paid exclusive attention. A consideration of the structure of IgE epitopes and their sequences, as well as a comprehensive understanding of the effects of various processes on epitopes and the impact of the gastrointestinal tract on them, can help target such issues. The current study focuses on the identified IgE epitopes in egg white proteins and evaluation of the effects of the gastrointestinal digestion, carbohydrate moiety, food matrix, microbial fermentation, recombinant allergen, heat treatment, Maillard reaction and combination of various processes and gastrointestinal digestion on egg white allergenicity. Although the gastrointestinal tract reduces the immunoreactivity of native egg white proteins, some of the IgE epitope-containing fragments remain intact during the digestion process. It has been found that the gastrointestinal tract can have both positive and negative impacts on the IgE binding activities of egg white proteins. Elimination of the carbohydrate moiety leads to a reduction in the immunoreactivity of ovalbumin. But, such effects from the carbohydrate parts in the IgE binding activity need to be explored further. In addition, the interaction between the egg white proteins and the food matrix leads to various effects from the gastrointestinal tract on the digestion of egg white proteins and their subsequent immunoreactivity. Further on this matter, studies have shown that both microbial fermentation and Maillard reaction can reduce the IgE binding activities of egg white proteins. Also, as an alternate approach, the thermal process can be used to treat the egg white proteins, which may result in the reduction or increase in their IgE binding activities depending on the conditions used in the process. Overall, based on the reported data, the allergenicity levels of egg white proteins can be mitigated or escalated depending on the conditions applied in the processing of the food products containing egg white. So far, no practical solutions have been reported to eliminate such allergenicity.

Sinomenine Relieves Airway Remodeling By Inhibiting Epithelial-Mesenchymal Transition Through Downregulating TGF-β1 and Smad3 Expression In Vitro and In Vivo

Airway remodeling is associated with dysregulation of epithelial-mesenchymal transition (EMT) in patients with asthma. Sinomenine (Sin) is an effective, biologically active alkaloid that has been reported to suppress airway remodeling in mice with asthma. However, the molecular mechanisms behind this effect remain unclear. We aimed to explore the potential relationship between Sin and EMT in respiratory epithelial cells in vitro and in vivo. First, 16HBE cells were exposed to 100 μg/mL LPS and treated with 200 μg/mL Sin. Cell proliferation, migration, and wound healing assays were performed to evaluate EMT, and EMT-related markers were detected using Western blotting. Mice with OVA-induced asthma were administered 35 mg/kg or 75 mg/kg Sin. Airway inflammation and remodeling detection experiments were performed, and EMT-related factors and proteins in the TGF-β1 pathway were detected using IHC and Western blotting. We found that Sin suppressed cell migration but not proliferation in LPS-exposed 16HBE cells. Sin also inhibited MMP7, MMP9, and vimentin expression in 16HBE cells and respiratory epithelial cells from mice with asthma. Furthermore, it decreased OVA-specific IgE and IL-4 levels in serum, relieved airway remodeling, attenuated subepithelial collagen deposition, and downregulating TGF-β1and Smad3 expression in mice with asthma. Our results suggest that Sin suppresses EMT by inhibiting IL-4 and downregulating TGF-β1 and Smad3 expression.

Enzymatic crosslinking and food allergenicity: A comprehensive review

Food allergy has become a major global public health concern. In the past decades, enzymatic crosslinking technique has been employed to mitigate the immunoreactivity of food allergens. It is an emerging non-thermal technique that can serve as a great alternative to conventional food processing approaches in developing hypoallergenic food products, owing to their benefits of high specificity and selectivity. Enzymatic crosslinking via tyrosinase (TYR), laccase (LAC), peroxidase (PO), and transglutaminase (TG) modifies the structural and biochemical properties of food allergens that subsequently cause denaturation and masking of the antigenic epitopes. LAC, TYR, and PO catalyze the oxidation of tyrosine side chains to initiate protein crosslinking, while TG initiates isopeptide bonding between lysine and glutamine residues. Enzymatic treatment produces a high molecular weight crosslinked polymer with reduced immunoreactivity and IgE-binding potential. Crosslinked allergens further inhibit mast cell degranulation due to the lower immunostimulatory potential that assists in the equilibration of T-helper (Th)1/Th2 immunobalance. This review provides an updated overview of the studies carried out in the last decade on the potential application of enzymatic crosslinking for mitigating food allergenicity that can be of importance in the context of developing hypoallergenic/non-allergenic food products.

N-glycans of bovine submaxillary mucin contain core-fucosylated and sulfated glycans but not sialylated glycans

Bovine submaxillary mucin (BSM) is a heavily-glycosylated macromolecular (approximately 4 MDa) protein and is used in various biomaterial applications in light of its high viscosity and biocompatibility, in addition to use as a biochemical substrate or inhibitor as a result of its abundant O-glycans. Although it has been reported that N-glycosylation provides stability of human mucins, most BSM research has been focused on its O-glycans, while N-glycans have not been reported to date. In this study, a common N-glycan core component was detected by monosaccharide analysis of BSM, and the structures of the N-glycans and their relative quantities were determined by liquid chromatography-tandem mass spectrometry. Seventeen N-glycans comprising ten complex-type [Fucose_0~2Hexose_3~4N-acetylhexosamine_1~6Sulfate_0~1; 61.1% (the sum of the relative quantities of each N-glycan out of the total N-glycans)], two high-mannose-type (Hexose_5~6N-acetylhexosamine₂; 12.0%), and five paucimannose type (Fucose_0~1Hexose_3~4N-acetylhexosamine_2~3; 26.9%) were identified, but no hybrid-type or sialylated N-glycans were found. Additionally, these are less-branched structures compared to human mucins. Of these, ten glycans (77.2%), including two sulfated glycans (8.0%), were core fucosylated, which confer unique biological functions to glycoproteins. The N-glycosylation sites were identified from the analysis of glycopeptides from BSM. This study is the first confirmation of N-glycan attachment to BSM.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

N-glycan in cockroach allergen regulates human basophil function

INTRODUCTION

Cockroach allergen exposure elicits cockroach sensitization and poses an increased risk for asthma. However, the major components in cockroach allergen and the mechanisms underlying the induction of cockroach allergen-induced allergy and asthma remain largely elusive. We sought to examine the role of cockroach-associated glycan in regulating human basophil function.

METHODS

N-linked glycans from naturally purified cockroach allergen Bla g 2 were characterized by MALDI-TOF mass spectrometry. Binding of cockroach allergen to serum IgE from cockroach allergic subjects was determined by solid-phase binding immunoassays. Role of cockroach associated glycan in histamine release and IL-4 production from human basophils was examined. Expression of C-type lectin receptors (CLRs) and their role in mediating glycan-uptake in the basophils was also investigated.

RESULTS

MALDI-TOF mass spectrometric analysis of N-glycan from Bla g 2 showed complex hybrid-types of glycans that terminated with mannose, galactose, and/or N-acetyl glucosamine (GlcNAc). Deglycosylated Bla g 2 showed reduced binding to IgE and was less capable of inducing histamine release from human basophils. In contrast, N-glycan derived from Bla g 2 significantly inhibited histamine release and IL-4 production from basophils passively sensitized with serum from cockroach allergic subjects. An analysis of CLRs revealed the expression of DC-SIGN and DCIR, but not MRC1 and dectin-1, in human basophils. Neutralizing antibody to DCIR, but not DC-SIGN, significantly inhibited Bla g 2 uptake by human basophils. A dose-dependent bindings of cockroach allergen to DCIR was also observed.

CONCLUSIONS

These observations indicate a previously unrecognized role for cockroach allergen-associated glycans in allergen-induced immune reactions, and DCIR may play a role in mediating the regulation of glycan on basophil function.

Rapid screening for specific glycosylation and pathogen interactions on a 78 species avian egg white glycoprotein microarray

There is an urgent need for discovery of novel antimicrobials and carbohydrate-based anti-adhesive strategies are desirable as they may not promote resistance. Discovery of novel anti-adhesive molecules from natural product libraries will require the use of a high throughput screening platform. Avian egg white (EW) provides nutrition for the embryo and protects against infection, with glycosylation responsible for binding certain pathogens. In this study, a microarray platform of 78 species of avian EWs was developed and profiled for glycosylation using a lectin panel with a wide range of carbohydrate specificities. The dominating linkages of sialic acid in EWs were determined for the first time using the lectins MAA and SNA-I. EW glycosylation similarity among the different orders of birds did not strictly depend on phylogenetic relationship. The interactions of five strains of bacterial pathogens, including Escherichia coli, Staphylococcus aureus and Vibrio cholera, identified a number of EWs as potential anti-adhesives, with some as strain- or species-specific. Of the two bacterial toxins examined, shiga-like toxin 1 subunit B bound to ten EWs with similar glycosylation more intensely than pigeon EW. This study provides a unique platform for high throughput screening of natural products for specific glycosylation and pathogen interactions. This platform may provide a useful platform in the future for discovery of anti-adhesives targeted for strain and species specificity.

Parasite molecules and host responses in cystic echinococcosis

Cystic echinococcosis is the infection by the larvae of cestode parasites belonging to the Echinococcus granulosus sensu lato species complex. Local host responses are strikingly subdued in relation to the size and persistence of these larvae, which develop within mammalian organs as 'hydatid cysts' measuring up to tens of cm in diameter. In a context in which helminth-derived immune-suppressive, as well as Th2-inducing, molecules garner much interest, knowledge on the interactions between E. granulosus molecules and the immune system lags behind. Here, we discuss what is known and what are the open questions on E. granulosus molecules and structures interacting with the innate and adaptive immune systems, potentially or in demonstrated form. We attempt a global biological approach on molecules that have been given consideration primarily as protective (Eg95) or diagnostic antigens (antigen B, antigen 5). We integrate glycobiological information, which traverses the discussions on antigen 5, the mucin-based protective laminated layer and immunologically active preparations from protoscoleces. We also highlight some less well-known molecules that appear as promising candidates to possess immune-regulatory activities. Finally, we point out gaps in the molecular-level knowledge of this infectious agent that hinder our understanding of its immunology.