Identification of N-Glycosites in Chicken Egg White Proteins Using an Omics Strategy

Integrated landscape of chicken egg chalaza proteomics

Chicken egg chalaza (CLZ) is a natural colloidal structure in eggs that exists as an egg yolk stabilizer and is similar in composition to egg white. In this study, the proteome, phosphoproteome, and N-glycoproteome of CLZ were characterized in depth. We hydrolyzed the CLZ proteins and enriched the phosphopeptides and glycopeptides. We identified 45 phosphoproteins and 80 N-glycoproteins, containing 59 phosphosites and 203 N-glycosylation sites, respectively. Typically, the ovalbumin in CLZ was both phosphorylated and N-glycosylated, with 4 phosphosites and 4 N-glycosylation sites. Moreover, we identified 2 N-glycosylated subunits of ovomucin, mucin-5B and mucin-6, with 32 and nine N- glycosylation sites, respectively. Analysis of the phosphorylation and N-glycosylation status of CLZ proteins could provide novel insights into the structural and functional characteristics of CLZ.

N-glycoproteomic profiling reveals structural and functional alterations in yellow primary preserved egg white under saline-alkali treatment

The posttranslational N-glycosylation of food proteins is important to their structure and function. However, the N-glycoproteomics of yellow preserved egg white were rarely reported. This study explored the changes of N-glycoproteome in yellow preserved eggs white after salt and alkali treatment. A total of 213 N-glycosites were identified on 102 glycoproteins, revealing prevalent glycosylation motifs and multiple N-glycosites within proteins. Salt and alkali treatment significantly altered the glycosylation patterns, impacting major proteins differently. GO analysis indicated the roles of differentially expressed glycoproteins in responding to stimuli and biological regulation. KEGG analysis emphasized the importance of salivary secretion pathway in enzyme secretion and peptide generation. Protein domain analysis highlighted the downregulation of Serpin. Protein-protein interaction networks revealed Apolipoprotein B as central players. This study provides essential structural information on the glycosylation modifications of egg white proteins, contributing to our understanding of the mechanisms behind the functional properties of preserved eggs.

Proteomic Analysis of Egg Yolk Proteins During Embryonic Development in Wanxi White Goose

To investigate the alterations of yolk protein during embryonic development in Wanxi white goose, the egg yolk protein composition at days 0, 4, 7, 14, 18, and 25 of incubation (D0, D4, D7, D14, D18, and D25) was analyzed by two-dimensional gel electrophoresis combined with mass spectrometry. A total of 65 spots representing 11 proteins with significant abundance changes were detected. Apolipoprotein B-100, vitellogenin-1, vitellogenin-2-like, riboflavin-binding protein, and serotransferrin mainly participated in nutrient (lipid, riboflavin, and iron ion) transport, and vitellogenin-2-like showed a lower abundance after D14. Ovomucoid-like were involved in endopeptidase inhibitory activity and immunoglobulin binding and exhibited a higher expression after D18, suggesting a potential role in promoting the absorption of immunoglobulin and providing passive immune protection for goose embryos after D18. Furthermore, myosin-9 and actin (ACTB) were involved in the tight junction pathway, potentially contributing to barrier integrity. Serum albumin mainly participated in cytolysis and toxic substance binding. Therefore, the high expression of serum albumin, myosin-9, and ACTB throughout the incubation might protect the developing embryo. Apolipoprotein B-100, vitellogenin-1, vitellogenin-2-like, riboflavin-binding protein, and serotransferrin might play a crucial role in providing nutrition for embryonic development, and VTG-2-like was preferentially degraded/absorbed.

Chicken egg white precipitates induced by water dilution

Chicken egg whites (whole egg white, EW; thick egg white, TKEW; thin egg white, TNEW) become turbid and are accompanied by the formation of precipitates after being diluted with an equal mass of deionized water. The precipitates of TKEW induced by water dilution (Thick Egg White Precipitates, TKEWP) account for 14.47 % of TKEW total dry matter, much higher than that of thin egg white precipitates (TNEWP) (1.51 %) and whole egg white precipitates (EWP) (5.53 %). Quantitative proteomic analysis identified 27 differentially abundant proteins (p < 0.05) among EW, EWP, TNEWP, and TKEWP. Lysozyme was found to be a key protein in the formation of EW precipitates induced by water dilution, as its abundance was significantly higher in TNEWP and TKEWP. Mucin-5B (α-ovomucin) had the highest abundance in TKEWP, suggesting that its insolubility is one of the important factors contributing to the large formation of TKEWP. This paper systematically studies the formation, characteristics, and composition of egg white precipitation caused by water dilution, and puts forward a new understanding of the processing characteristics of egg white liquid, thus laying a theoretical foundation for further research methods to reduce egg white precipitation by water dilution.

Underlying mechanisms of egg white thinning in hot spring eggs during storage: Weak gel properties and quantitative proteome analysis

As a weakly gelling protein, hot spring egg white underwent thinning during storage. This study explored the mechanism of thinning in hot spring egg white from the perspective of "gel structure and protein composition" using quantitative proteomics, SEM, SDS-PAGE, and other techniques. Quantitative proteomics analysis showed that there were 81 (44 up-regulated and 21 down-regulated) key proteins related to thinning of hot spring egg white. The changes in the relative abundance of proteins such as ovalbumin-related Y, mucin-6, lysozyme, ovomucoid, and ovotransferrin might be important reasons for thinning in hot spring egg white. SEM results indicated that the gel network gradually became regular and uniform, with large pores appearing on the cross-section and being pierced. Along with the decrease in intermolecular electrostatic repulsion, protein molecules gradually aggregated. The particle size gradually increased from 139.1 nm to 422.5 nm. Meanwhile, the surface hydrophobicity, and disulfide bond content gradually increased. These changes might be the reasons for thinning in hot spring egg white during storage. It can provide a new perspective for studying the thinning mechanism of weakly gelling egg whites.

Exploring the binding effect and mechanism of glycyrrhizin to ovomucin by combining spectroscopic analysis and molecular docking

Ovomucin (OVM) is an ideal natural macromolecular glycoprotein extracted from eggs with good adhesion. Based on the defect that glycyrrhizin (GL) has good antiviral activity but fast metabolism, this study aimed to explore the binding effect and mechanism of GL to OVM, using multi-spectroscopic techniques, isothermal titration calorimetry (ITC), and molecular docking. The adhesion ability of OVM to the hydrophilic interface and GL was first demonstrated by dual polarization interferometry (DPI) analysis and binding capacity assay, and the OVM-GL complex exhibited a similar affinity for the spike protein of COVID-19. The spectroscopic results show that GL can quench the inherent fluorescence and change the glycosidic bond and secondary structure of OVM. The ITC measurements suggested that the binding was exothermic, the hydrogen bond was the dominant binding force for forming OVM-GL. Finally, molecular docking results indicated that GL has hydrogen bond interaction with several amino acid residues located in α-OVM and β-OVM while embedding into the hydrophobic pocket of OVM via hydrophobic interactions. In conclusion, OVM can adhere to the hydrophilic interface and bind to GL through hydrogen bonding and hydrophobic interactions to form a stable complex, that is expected to be helpful in virus prophylaxis.

Quantitative N-Glycoproteomic Analysis of Cattle-Yak and Yak Longissimus Thoracis

In this study, the N-glycosylated protein profiles of cattle-yak longissimus thoracis (CYLT) and yak longissimus thoracis (YLT) were comparatively analyzed using quantitative proteomics techniques. A total of 76 differential N-glycosylated proteins (DGPs) were screened from 181 quantified N-glycoproteins, indicating that differences in N-glycosylation levels are key to the differences between CYLT and YLT. In particular, a variety of N-glycoproteins involved in the extracellular matrix were differentially N-glycosylated between CYLT and YLT, mainly including fibrillin-1, fibromodulin, collagen, and laminins. In addition, the N-glycosylation levels of several lysosomal-related proteolytic enzymes (cathepsin D, dipeptidyl peptidase 1, legumain, and aminopeptidases, etc.) were significantly higher in CYLT. These results indicated that the N-glycosylation of CYLT and YLT proteins plays a crucial role in the regulation of extracellular matrix organization (muscle fiber structure) and lysosomal activity (postmortem meat tenderness). The results remind us that posttranslation modifications, especially N-glycosylation, are still icebergs beneath the surface.

Comparative N-Glycoproteomic Investigation of Eggshell Cuticle and Mineralized Layer Proteins

The eggshell cuticle layer (ECL) and eggshell mineralized layer (EML) contain amounts of glycoproteins and proteoglycans. However, there were few comprehensive reports about the effect of post-translational modifications on protein structure and function which requires investigation. Therefore, we used comparative N-glycoproteomics to study glycoproteins in the ECL and EML. We identified a total of 272 glycoproteins in this experiment and found that glycoproteins located in EML were more than that in ECL. Moreover, they showed distinct functional difference between both layers. As N-glycosylation of ovocleidin-17 and ovocleidin-116 in the EML affected eggshell mineralization, some glycoproteins located in ECL, like ovotransferrin and ovostatin-like, possessed antibacterial activity. The several regulated glycoproteins in the EML may pertain to the regulation of mineralization, while glycosylated proteins in the ECL may contribute to molecular adhesion and defense against microbial invasion. This study provides new insights into the eggshell matrix protein contents of the ECL and EML.

Antigen presentation induced variation in ovalbumin sensitization between chicken and duck species

The difference in the allergenicity of chicken ovalbumin (C-OVA) and duck ovalbumin (D-OVA) can be related to their differences in antigen presentation. This study explored the differences in uptake between C-OVA and D-OVA through fluorescence dye-labeling, DC antigen presentation, and the immune response of T cells by using C-OVA and D-OVA allergic animal and cell models. The ileum DCs of mice in the C-C group took up more C-OVA than that of D-D and C-D groups through in vivo imaging. Furthermore, C-OVA induced the maturation of DCs in mice in the C-C group as shown in the up-regulation of the expressions of MHC II, CD86 and CD80 on the surface of DCs, and enhanced the ability of antigen presentation. In addition, C-OVA induced the maturation of DCs, promoted the differentiation of T cells into Th2 cells, increased the secretion of the cytokine IL-4 and specific antibody s-IgE, and thus generated an immune response. However, sensitized and cross sensitized D-OVA (D-D and C-D groups) couldn't induce the maturation of DCs, and induced less differentiation of T cells and lower secretion of cytokines compared to C-OVA. In conclusion, the differences in antigen presentation was one of the important factors resulting in the differences in the sensitization between C-OVA and D-OVA.

Preparation of an LZ-OEO Compound Antibacterial Gel and the Effect of Microwave Treatment on Its Structure and Stability

Composite gels prepared with ovalbumin (OVA) as basic materials have been gradually utilized in food and biological fields. However, the structure and function of gels made from natural materials are not perfect, especially the hardness, viscoelasticity and water-holding capacity of gels, which are easily affected by various factors (pH, NaCl, etc.). In order to improve the antibacterial effect and safety of gels, and on the basis of exploring the bacteriostatic formula of lysozyme-oregano essential oil (LZ-OEO), the influence of microwave treatment on the stability of the composite bacteriostatic material gel was emphatically investigated and discussed so as to develop a new bacteriostatic gel material. The results revealed that the LZ-OEO antibacterial gel prepared by adding 20% OEO, with a ratio of 3:2 between OVA and LZ, was more stable after microwave treatment, and the synergistic antibacterial effect was significantly improved. That is, the OVA and LZ-OEO composite gel processed using a 350 W microwave treatment for 1 min had the highest hardness, the water-holding capacity reached 78.05% and a dense and ordered network structure was formed. In addition, the compound gel displayed excellent antibacterial effects against Staphylococcus aureus and Escherichia coli. The experimental findings in this study effectively expands the application scope of lysozyme antibacterial materials and provides a more favorable technical foundation for future development and utilization.

Unveiling and application of the chicken egg proteome: An overview on a two-decade achievement

Egg proteins are not only the most complete and ideal form of protein for human or embryo nutrition but also play the vital role in the food industry. Egg proteins are subjected to many potential changes under various conditions, which may further alter the nutritional value, physicochemical-properties, and bioactivities of proteins. Recent advances in our understanding of the proteome of raw egg matrix from different species and dynamic changes occurring during storage and incubation are developing rapidly. This review provides a comprehensive overview of the main characteristics of chicken egg proteome, covering all its components and applications under various conditions, such as markers detection, egg quality evaluation, genetic and biological unknown identification, and embryonic nutritional supplementation, which not only contributes to our in-depth understanding of each constituent functionality of proteome, but also provides information to increase the value to egg industry.

Formation mechanism of high-viscosity gelatinous egg white among "Fenghuang Egg": Phenomenon, structure, and substance composition

"Fenghuang Egg" is a special egg product incubated for 12 days by fertilized hen eggs. Its egg white contains high-viscosity and excellent thermal gel strength. A comparative study on the differences in gel properties, structure, and substance composition between fresh egg white (FEW) and "Fenghuang egg" gelatinous egg white (GEW) was carried out. Experimental results showed GEW had better apparent viscosity, as well as the hardness, cohesiveness and water holding capacity (WHC) of thermal gel; the content and size of aggregate structure increased significantly in GEW, and a fibrous dense network composed of numerous spherical nanoparticles connected in series was formed after heating. In addition, it also discovered that more water molecules in GEW existed in the form of bound water. A total of 41 proteins changed significantly in FEW and GEW, Mucin 6 might be the main reason for the enhanced viscosity of GEW, and OVA might be the dominant protein differentiating the thermal gel properties between FEW and GEW. This study revealed that the differences in gel properties and structures between FEW and GEW were closely related to the content of highly glycosylated globular proteins, laying a theoretical foundation for the application of high-viscosity egg whites.

Comparative Study on the Characterization of Myofibrillar Proteins from Tilapia, Golden Pompano and Skipjack Tuna

In this study, the physicochemical properties, functional properties and N-glycoproteome of tilapia myofibrillar protein (TMP), golden pompano myofibrillar protein (GPMP) and skipjack tuna myofibrillar protein (STMP) were assessed. The microstructures and protein compositions of the three MPs were similar. TMP and GPMP had higher solubility, sulfhydryl content and endogenous fluorescence intensity, lower surface hydrophobicity and β-sheet contents than STMP. The results showed that the protein structures of TMP and GPMP were more folded and stable. Due to its low solubility and high surface hydrophobicity, STMP had low emulsifying activity and high foaming activity. By N-glycoproteomics analysis, 23, 85 and 22 glycoproteins that contained 28, 129 and 35 N-glycosylation sites, were identified in TMP, GPMP and STMP, respectively. GPMP had more N-glycoproteins and N-glycosylation sites than STMP, which was possibly the reason for GPMP’s higher solubility and EAI. These results provide useful information for the effective utilization of various fish products.

Effect of glycation degree on the structure and digestion properties of ovalbumin: A study of amino acids and peptides release after in vitro gastrointestinal simulated digestion

Glycation can improve the functional properties of protein. However, in vitro and animal studies have shown that glycation induced lysine blockage and impaired protein digestibility. This study aimed to explore the effects of different glycation degree on the structure and digestive characteristics of ovalbumin. The results showed that glycation decreased the turbidity and hydrophobicity of the protein and changed the protein structure. Moreover, the results of in vitro simulated digestion revealed that glycation reduced the contents of essential amino acids and total amino acids after digestion. Glycation changed the amino acids and peptides release from the protein by resisting the digestion of digestive enzymes, especially trypsin. In conclusion, this work links glycation, protein digestibility, and the release of amino acids and peptides. This emphasizes the importance of the balance between improving properties and ensuring the digestibility of proteins during food processing.

Integrated proteomic, phosphoproteomic, and N-glycoproteomic analyses of the longissimus thoracis of yaks

Yaks (Bos mutus) live in the Qinghai–Tibet plateau. The quality of yak meat is unique due to its genetic and physiological characteristics. Identification of the proteome of yak muscle could help to reveal its meat-quality properties. The common proteome, phosphoproteome, and N-glycoproteome of yak longissimus thoracis (YLT) were analyzed by liquid chromatography-tandem mass spectrometry-based shotgun analysis. A total of 1812 common proteins, 1303 phosphoproteins (3918 phosphorylation sites), and 204 N-glycoproteins (285 N-glycosylation sites) were identified in YLT. The common proteins in YLT were involved mainly in myofibril structure and energy metabolism; phosphoproteins were associated primarily with myofibril organization, regulation of energy metabolism, and signaling; N-glycoproteins were engaged mainly in extracellular-matrix organization, cellular immunity, and organismal homeostasis. We reported, for the first time, the “panorama” of the YLT proteome, specifically the N-glycoproteome of YLT. Our results provide essential information for understanding post mortem physiology (rigor mortis and aging) and the quality of yak meat.

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A total of 2650 proteins were identified in yak longissimus thoracis.

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Common proteins were involved mainly in myofibril structure and energy metabolism.

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Phosphoproteins were associated with myofibrils, energy metabolism, and signaling.

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N-glycoproteins were engaged mainly in ECM organization, immunity, and homeostasis.

Quantitative N-glycoproteome analysis of bovine milk and yogurt

Post-translational modification structure of food's proteins might be changed during processing, thereby affecting the nutritional characteristics of the food product. In this study, differences in protein N-glycosylation patterns between milk and yogurt were quantitatively compared based on glycopeptide enrichment, liquid chromatography separation, and tandem mass spectrometry analysis. A total of 181 N-glycosites were identified, among which 142 were quantified in milk and yogurt. Significant alterations in the abundance of 13 of these N-glycosites were evident after the fermentation of milk into yogurt. Overall, the N-glycosylation status of the majority of milk proteins remained relatively unchanged in yogurt, suggesting that their conformations, activities, and functions were maintained despite the fermentation process. Among the main milk proteins, N²⁴¹ of cathepsin D and N³⁵⁸ of lactoperoxidase were markedly reduced after undergoing lactic acid fermentation to produce yogurt. Furthermore, a comparative analysis of current and previously reported N-glycoproteomic data revealed heterogeneity in the N-glycosylation of milk proteins. To sum up, a quantitative comparison of the N-glycoproteomes of milk and yogurt was presented here for the first time, providing evidence that the fermentation process of yogurt could cause changes in the N-glycosylation of certain milk proteins.

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181 N-glycosites from 118 N-glycoproteins were identified in milk and yogurt.

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13 N-glycosites changed significantly after fermentation of milk into yogurt.

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N²⁴¹ of cathepsin D and N³⁵⁸ of lactoperoxidase was markedly reduced in yogurt.

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Heterogeneity of N-glycosylation of milk protein has been documented.

Quantitative proteomic analyses during formation of chicken egg yolk

A quantitative comparison of the proteomes during different periods of the formation of egg yolk, from yellow follicles (YF), small hierarchical follicles (9-12 mm, SF), and the largest hierarchical follicle (LF), was performed. The abundance of major egg yolk proteins (apolipoprotein B and vitellogenins) changed significantly during the yolk formation, and several protein hydrolases and isomerases, which may be related to the processing of egg yolk proteins, also varied significantly. The binding proteins for three vitamins (retinol, riboflavin, and vitamin D) and cholesterol were all most abundant in the LF period, suggesting that these nutrients were transported mainly at the final period of the egg yolk formation. Immunoglobulins decreased and complement proteins increased as formation progressed, indicating the dynamic nature of the egg yolk immune system. These results are helpful for understanding the nutrient composition, the formation of assembly structure, the preservation and processing properties of egg yolk.

Comparative N-glycoproteomic analysis of Tibetan and lowland chicken fertilized eggs: Implications on proteins biofunction and species evolution

The characterization and functionality of protein glycosylation among different related species are of common interest. Herein, non-standard quantification and N-glycosylation enrichment technology combined with ultra-high liquid chromatography-tandem mass spectrometry were used to establish detailed N-glycoproteomics of fertilized eggs, and quantitatively compared between Tibetan and lowland chicken. A total of 396N-glycosites from 143 glycoproteins were found. Specifically, compared with lowland chicken egg white, 32N-glycosites of 22 glycoproteins were up-regulated and 57N-glycosites of 25 glycoproteins were down-regulated in Tibetan chicken egg white. Also, 137N-glycosites in 72 glycoproteins showed much higher-degree glycosylation and 36N-glycosites in 15 glycoproteins displayed lower-degree glycosylation in Tibetan chicken egg yolk than those in lowland chicken egg yolk. Through bioinformatic analysis, these varied glycoproteins were highly associated with antifreeze activity, hypoxia adaptation, coagulation cascade, and binding/immunity activities, which may be related to plateau hypoxia and cold stress. PRACTICAL APPLICATIONS: These findings provide a new insight on the role of biological egg N-glycoproteins related to environmental adaptation and evolution, which may be further applied in improving egg processing and human health, by developing biomolecules for food and medical industry.

Plasma membrane N-glycoproteome analysis of wheat seedling leaves under drought stress

Protein glycosylation is one of the ubiquitous post-translational modifications in eukaryotic cells, which play important roles in plant growth and adverse response. In this study, we performed the first comprehensive wheat plasma membrane N-glycoproteome analysis under drought stress via glycopeptide HILIC enrichment and LC-MS/MS identification. In total, 414 glycosylated sites corresponding to 407 glycopeptides and 312 unique glycoproteins were identified, of which 173 plasma membrane glycoproteins with 215 N-glycosylation sites were significantly regulated by drought stress. Functional enrichment analysis reveals that the significantly regulated N-glycosylation proteins were particularly related to protein kinase activity involved in the reception and transduction of extracellular signal and plant cell wall remolding. The motifs and sequence structures analysis showed that the significantly regulated N-glycosylation sites were concentrated within [NxT] motif, and 79.5% of them were located on the random coil that is always on the protein surface and flexible regions, which could facilitate protein glycosylated modification and enhance protein structural stability via reducing protein flexibility. PNGase F enzyme digestion and glycosylation site mutation further indicated that N-glycosylated modification could increase protein stability. Therefore, N-glycosylated modification is involved in plant adaptation to drought stress by improving the stability of cell wall remodeling related plasma membrane proteins.

Recent Progress on Protein-Polyphenol Complexes: Effect on Stability and Nutrients Delivery of Oil-in-Water Emulsion System

Oil-in-water emulsions are widely encountered in the food and health product industries. However, the unsaturated fatty acids in emulsions are easily affected by light, oxygen, and heat, which leads to oxidation, bringing forward difficulties in controlling emulsion quality during transportation, storage, and retail. Proteins are commonly used as emulsifiers that can enhance the shelf, thermal and oxidation stability of emulsions. Polyphenols are commonly found in plants and members of the family have been reported to possess antioxidant, anticancer, and antimicrobial activities. Numerous studies have shown that binding of polyphenols to proteins can change the structure and function of the latter. In this paper, the formation of protein-polyphenol complexes (PPCs) is reviewed in relation to the latters' use as emulsifiers, using the (covalent or non-covalent) interactions between the two as a starting point. In addition, the effects polyphenol binding on the structure and function of proteins are discussed. The effects of proteins from different sources interacting with polyphenols on the emulsification, antioxidation, nutrient delivery and digestibility of oil-in-water emulsion are also summarized. In conclusion, the interaction between proteins and polyphenols in emulsions is complicated and still understudied, thereby requiring further investigation. The present review results in a critical appraisal of the relevant state-of-the-art with a focus on complexes' application potential in the food industry, including digestion and bioavailability studies.

Ovomucin may be the key protein involved in the early formation of egg-white thermal gel

Clarification of the mechanism of heat-induced gel formation by proteins under natural food systems could provide important references for the regulation of food texture. In the present study, the proteins involved in the early stage (heating at 72 °C for 8 min) of egg-white thermal gel (EWG) formation were studied quantitatively through comparative proteomic analysis. We discovered that the abundance of ovalbumin and ovomucoid increased significantly (p < 0.01), whereas that of ovotransferrin, lysozyme, ovomucin (mucin 5B and mucin 6) decreased significantly (p < 0.01), in the supernatant of EWG. If the initial interaction of egg white proteins was altered by ultrasonic pretreatment, the abundance of ovomucin and lysozyme in the supernatant of EWG increased, and was accompanied by the change from a solid gel to a fluid gel. Based on these results, we hypothesize that ovomucin has a key role in the formation and regulation of EWG properties.

Comparative N-Glycoproteomic Analysis Provides Novel Insights into the Deterioration Mechanisms in Chicken Egg Vitelline Membrane during High-Temperature Storage

The weakening of chicken egg vitelline membrane (CEVM) is one of the most important factors influencing egg quality during high-temperature storage. Therefore, a comparative N-glycoproteomic analysis of CEVM after 10 days of storage at 30 °C was performed to explore the roles of protein N-glycosylation in membrane deterioration. In total, 399 N-glycosites corresponding to 198 proteins were identified, of which 46 N-glycosites from 30 proteins were significantly altered. Gene ontology analysis revealed that these differentially N-glycosylated proteins (DGPs) were involved in antibacterial activity, glycosaminoglycan binding, lipid binding, and aminopeptidase activity. Removal of the N-glycans in Mucin-5B may result in a loss of CEVM's mechanical properties. The N-glycosites enriched in the apolipoprotein B β2 domain in CEVM were significantly changed, which may contribute to lipid composition modifications during storage. Moreover, N-glycosites in several metalloproteases were located within the functional domain or active site region, indicating that the decreased N-glycosylation levels may affect their structural stability, specific substrate binding, or enzyme activity. These findings provide novel insights into the roles of protein N-glycosylation during membrane weakening.

Phosvitin phosphopeptides produced by pressurized hea-trypsin hydrolysis promote the differentiation and mineralization of MC3T3-E1 cells via the OPG/RANKL signaling pathways

Phosvitin (PV) from egg yolk is an excellent substrate for the production of phosphopeptides, which have a strong calcium chelating capacity and promoting calcium absorption and bone mineralization. This study investigated the effect of PV hydrolysates produced using a effective preparation method (high temperature (121°C) and mild pressure (0.1 MPa), HTMP) or HTMP pretreatment and trypsin hydrolysis combination (HTMP-PV18) on the physiology of an osteoblast MC3T3-E1 cells line. The proliferation, apoptosis, and differentiation of MC3T3-E1 cells were analyzed using the CCK-8, flow cytometry, and RT-PCR reactions, respectively. Both the HTMP-PV and HTMP-PV18 increased the proliferation, and inhibited the apoptosis of MC3T3-E1 cells significantly. The HTMP-PV increased the proliferation of MC3T3-E1 cells by 147.12 ± 2.11% and the HTMP-PV18 by 136.43 ± 4.51%. In addition, the HTMP-PV and HTMP-PV18 effectively promoted the expression of genes related to the OPG/RANKL signaling channel during cell differentiation. This indicated that both the HTMP-PV and HTMP-PV18 have the potential to promote bone mineralization by improving the proliferation and differentiation of osteoblastic cells.

Phosphoinositide signaling plays a key role in the regulation of cell wall reconstruction during the postharvest morphological development of Dictyophora indusiata

The potential signaling mechanism of Dictyophora indusiata during postharvest morphological development was investigated through quantitative phosphoproteomic analyses. A total of 1566 phosphorylation sites changed significantly (872 upregulated and 694 downregulated) in the mature stage compared with those in the peach-shaped stage of D. indusiata. Bioinformatics analysis showed that the upregulated differentially phosphorylated proteins were mainly involved in the "phosphatidylinositol signaling system" and "mitogen-activated protein kinase signaling pathway-yeast", while the downregulated differentially phosphorylated proteins were related mainly to "starch and sucrose metabolism". Further mining of the phosphoproteome data revealed that upregulated phosphoinositide signaling activated the cell wall integrity pathway and then regulated the synthesis of the main components of the cell wall. The results suggested that phosphoinositide signaling could be a potential target pathway for the regulation of the postharvest morphological development of D. indusiata.

A puzzle piece of protein N-glycosylation in chicken egg: N-glycoproteome of chicken egg vitelline membrane

The chicken egg vitelline membrane (CEVM) is an important structure for the transmembrane transport of egg yolk components, protection of the blastodisc, and separation of egg white and egg yolk. In this study, the N-glycoproteome of the CEVM was mapped and analyzed in depth. Total protein of the CEVM was digested, and the glycopeptides were enriched by a hydrophilic interaction liquid chromatography microcolumn and identified by nano liquid chromatography/tandem mass spectrometry. A total of 435 N-glycosylation sites on 208 N-glycoproteins were identified in CEVM. Gene Ontology enrichment analysis showed that CEVM N-glycoproteins are mainly involved in the regulation of proteinases/inhibitors and transmembrane transport of lipids. Mucin-5B is the primary N-glycoprotein in the CEVM. Comparison of the main N-glycoproteins between the CEVM and other egg parts revealed the tissue specificity of N-glycosylation of egg proteins. The results provide insights into protein N-glycosylation in the chicken egg, CEVM functions and underlying mechanisms.

Integrated proteomic, phosphoproteomic and N-glycoproteomic analyses of chicken eggshell matrix

Eggshell matrix (EM) proteins play an important biological role in eggshell mineralization and embryo development. Many studies have demonstrated that some matrix proteins undergo posttranslational modifications, including phosphorylation and glycosylation, which have important regulatory effects on the functional properties of the proteins. Systematic analysis of the proteome, the phosphorylated modified proteome and the glycosylated modified proteome of the chicken EM was performed using a proteomics strategy. A total of 112 phosphorylation sites from 69 phosphoproteins and 297 N-glycosylation sites from 182 N-glycoproteins were identified in the chicken EM. Among all these identified modified proteins, 129 were not identified in the proteome (547 proteins). Therefore, a total of 676 EM proteins were identified in this study. Gene ontology (GO) enrichment analysis indicated that EM proteins and phosphoproteins were mainly enriched in regulation of enzyme activity, while EM N-glycoproteins were enriched in immune response regulation.

Structural and antimicrobial properties of Maillard reaction products in chicken liver protein hydrolysate after sonication

This study aimed to investigate the structural and antimicrobial properties of Maillard reaction products (MRPs) in chicken liver protein (CLP) and its hydrolysate (CLPH) after sonication (SCLPH). The MRPs of CLP (CLPM), CLPH (CLPHM) and SCLPH (SCLPHM) were analyzed by several spectrometric techniques. The molecular weights of the CLPHM and SCLPHM were primarily between 1.35 kDa and 17 kDa. Moreover, the molecular weights in the CLPHM and SCLPHM below 1.35 kDa were increased, which indicated that cross-linking and thermal degradation occurred during the Maillard reaction (MR). The SCLPHM showed an obvious network skeleton, and the surface had many small crystal-shaped particles after ultrasound treatment and MR by scanning electron microscopy. The SCLPHM had more negative charges than the CLPHM, thus effectively inhibiting the growth of S. saprophyticus and E. coli. MR and ultrasound treatment could be a promising technology to expand the application prospects of low-value meat byproducts.

Quantitative N-glycoproteomic analyses provide insights into the effects of thermal processes on egg white functional properties

This study tries to elucidate the different mechanisms of functional properties among pasteurized egg white (P-EW), spray-dried egg white (SD-EW) and fresh egg white (F-EW) via quantitative N-glycoproteomic analyses. The results showed that spray-drying increased the surface hydrophobicity (181.4%) and zeta potential (25.6%) of egg white, which contributed to the enhancement of emulsifying activity index (20.1%) and foaming capacity (35.2%). Pasteurization caused the disintegration of natural protein aggregates in F-EW and resulted in a "block-like" P-EW gel and higher water holding capacity (6.2%). Spray-drying caused formation of thermal aggregates and led to a "mesh-like" SD-EW gel and better cohesiveness (3.6%). Quantitative N-glycoproteomic analysis showed that the abundance of 32 N-glycosites from 18 N-glycoproteins (such as Mucin 5B) of SD-EW was significantly reduced comparing to F-EW, indicated that the N-glycans of egg white protein are likely to be covalently cross-linked during spray-drying and are involved in thermal aggregation.

Omics analysis of holoproteins and modified proteins of quail egg

Confirmed to be a new type of food resource, quail egg can provide humans with high-quality protein and offer various nutrients that can promote growth and development. Post-translational modification of proteins can regulate their molecular structures and physiological functions. However, the understanding and related research of quail egg holoproteins and post-translationally modified proteins is not yet sufficient. This study provides an in-depth analysis of quail egg proteins using an omics strategy. A total of 175 proteins, 109 N-glycoproteins (293 N-glycosylation sites) and 23 phosphoproteins (84 phosphorylation sites) were identified. Motif analysis showed that N-glycosylation sites of quail eggs were classical sites. The main characteristic sequence of the phosphorylation site is "S-X-E" (77%). Functional analysis indicated that quail egg proteins, modified proteins were enriched in the regulation of enzyme activity. These results have significant reference value for understanding the structure, function of quail eggs, explaining the physicochemical reaction during the storage.

Quantitative Comparative Proteomic Analysis of Chicken Egg Vitelline Membrane Proteins during High-Temperature Storage

To explore the thermally induced alterations in chicken egg vitelline membrane (CEVM) protein abundances, a comparative proteomic analysis of CEVM after 10 days of storage at 30 °C was performed. Altogether, 981 proteins were identified, of which 124 protein abundances were decreased and 79 were increased. Bioinformatic analysis suggested that the altered proteins were related to structure (n = 10), mechanical properties (n = 13), chaperone (n = 15), antibacterial (n = 12), and antioxidant (n = 3). Alterations in abundances of structural proteins, possibly resulting from the disintegration of these complexes, were observed in this study, suggesting a loss in fibrous structure. Several proteins involved in mechanical strength (n = 10), elasticity (n = 3), and chaperone were decreased in abundances, which indicated that deficits in these proteins might affect the CEVM mechanical properties. These findings will extend our understanding of CEVM deterioration during high-temperature storage from a proteomic perspective.

Simultaneous separation of the four major allergens of hen egg white

Hen egg is a worldwide top-consumed food that has attracted public health concerns because it can induce allergic reactions in sensitized individuals. Food allergy investigations need highly purified egg allergens. However, a limited number of purification methods have been described for the combined separation of more than two egg allergens and only few of them have evaluated the immunological activity of these purified proteins. The aim of this work was to develop a chromatographic method for the separation of the four major egg allergens (ovomucoid, ovalbumin, ovotranferrin, and lysozyme) with a demonstrated immunological activity. After a pre-processing step for ovomucin precipitation and pH adjustment, remaining egg white proteins were loaded onto CM-Sepharose column and major egg allergens were separated using cation-exchange chromatography. Yield of ovomucoid, ovalbumin, ovotranferrin, and lysozyme was 60.0%, 52.1%, 29.6%, and 90.2%, respectively. Purified allergens were compared with their commercial standards, showing a high purity as well as a maintained antigenicity. The protocol described in this work is simple, quick, low-cost, and suitable for the study of the immunological properties of these allergens. For higher ovalbumin demand in the lab, 2.1 g ovalbumin can be produced in a single process with high purity.

A Comprehensive Identification of Chicken Egg White Phosphoproteomics Based on a Novel Digestion Approach

There are plenty of phosphoproteins in chicken egg white (CEW), which are of great significance for the biological activity and function of CEW. In this study, phosphorylated proteins in CEW were identified and analyzed based on two digestion strategies (trypsin and trypsin/glutamyl endoproteinase). Besides, the enrichment strategy of immobilized metal affinity chromatography was used, and phosphopeptides were identified by nano liquid chromatography/tandem mass spectrometry. A total of 189 phosphosites mapped onto 166 phosphopeptides corresponding to 96 phosphoproteins were identified. Gene ontology analysis suggested that these phosphoproteins of CEW mainly participated in biological processes such as "cell process", "biological regulation", and "response to stimulus". Moreover, the phosphoproteins of CEW were involved in molecular functions, primarily including "binding" and "catalytic activity". On the basis of the available literature, the research was the first comprehensive identification of chicken egg white phosphoproteins. This study further enriched the identification of phosphoproteins in CEW and laid a foundation for the subsequent study of phosphoproteins.

Quantitative proteomic and metabolomic analysis of Dictyophora indusiata fruiting bodies during post-harvest morphological development

The differences in Dictyophora indusiata fruiting bodies between peach-shaped and mature stage during the postharvest were systematically investigated through quantitative proteomic and metabolomic analyses. A total of 951 differentially expressed proteins were identified, 571 upregulated and 380 downregulated in the mature fruiting body; additionally, 173 upregulated and 165 downregulated differential abundance metabolites were screened. Integrated proteome and metabolome analyses showed that, during the maturation of D. indusiata fruiting bodies, glycerophospholipids were hydrolyzed and drastically decreased, the degradation of glucan was upregulated, the degradation and synthesis of chitin were simultaneously enhanced, and proteins were dominated via catabolism. Along with vigorous material metabolism, energy production was enhanced through the upregulated TCA-cycles and oxidative phosphorylation. In addition, the synthesis of antioxidant substances and the decomposition of peroxides were enhanced in mature fruiting bodies. These omics analyses of D. indusiata provide high-throughput data and reveal the changes in the post-harvest morphological development.

A comparative study of the modulation of the gut microbiota in rats by dietary intervention with different sources of egg-white proteins

BACKGROUND

Gut microflora dysbiosis has been related closely to a variety of diseases including obesity and inflammatory bowel disease. Proteins and peptides in egg white have been found to alleviate inflammation but the role played by the intestinal flora is still unclear. Using casein as a dietary protein control, we investigated the effects of diets composed of hen egg white, duck egg white, and preserved egg white on gut microbiota in the rat cecum.

RESULTS

The gut microbiota in rats were altered after egg-white consumption. The results showed that rats fed with egg white had a similar overall structure of cecal bacterial communities, which was different from those fed with casein. The relative abundance of Akkermansia in the group of rats fed with hen egg white was highest among all groups. Rats fed with duck egg white had significantly higher relative abundance of Proteobacteria and Peptostreptococcaceae, and lower relative abundance of Lachnospiraceae. In addition, the levels of lipopolysaccharide (LPS) and lipopolysaccharide-binding protein (LBP) in rats fed with duck egg white and preserved egg white were lower than the levels in rats fed with hen egg white.

CONCLUSION

Our results indicated the possible positive effect on homeostasis of the intestinal flora brought about by the intake of duck egg white. This study provides an insight into the potential positive impact of preserved egg white on health by changing gut microbiota and affecting the antigen load. © 2020 Society of Chemical Industry.

Potential role of ovomucin and its peptides in modulation of intestinal health: A review

Intestinal dysfunction, which may cause a series of metabolic diseases, has become a worldwide health problem. In the past few years, studies have shown that consumption of poultry eggs has the potential to prevent a variety of metabolic diseases, and increasing attention has been directed to the bioactive proteins and their peptides in poultry eggs. This review mainly focused on the biological activities of an important egg-derived protein named ovomucin. Ovomucin and its derivatives have good anti-inflammatory, antioxidant, immunity-regulating and other biological functions. These activities may affect the physical, biological and immune barriers associated with intestinal health. This paper reviewed the structure and the structure-activity relationship of ovomucin，the potential role of ovomucin and its derivatives in modulation of intestinal health are also summarized. Finally, the potential applications of ovomucin and its peptides as functional food components to prevent and assist in the pretreatment of intestinal health problems are prospected.

Molecular aggregation and property changes of egg yolk low-density lipoprotein induced by ethanol and high-density ultrasound

Solvent and physical treatment are widely used in egg yolk processing, but the detailed changes in the molecular structure of egg yolk proteins during processing are unclear. The aim of this study was to investigate the effects of ethanol and ultrasonic treatments on chicken egg yolk low-density lipoprotein (LDL). The solubility, emulsifying activity and emulsifying stability decreased by 74.75%, 46.91%, and 81.58% after ethanol treatment, respectively. The average particle size of ethanol-treated LDL increased 13.3-fold to 937.85 nm. These results suggested that ethanol treatment induced wide-ranging aggregation of LDL. In contrast to ethanol treatment, ultrasonic treatment promoted the solubility and emulsifying stability of LDL and enhanced its zeta-potential (119.56%) and surface hydrophobicity (10.81%). Based on particle size analysis and transmission electron microscopy, approximately 34.65% of LDL had undergone aggregation and the molecular interface became more flexible after ultrasonic treatment. These results revealed the detailed changes in egg yolk LDL structure and properties during solvent (ethanol) and physical (ultrasound) processing.