Separation and identification of hen egg protein isoforms using SDS–PAGE and 2D gel electrophoresis with MALDI-TOF mass spectrometry

Analytical approaches for assessing protein structure in protein-rich food: A comprehensive review

This review focuses on changes in nutrition and functional properties of protein-rich foods, primarily attributed to alterations in protein structures. We provide a comprehensive overview and comparison of commonly used laboratory methods for protein structure identification, aiming to offer readers a convenient understanding of these techniques. The review covers a range of detection technologies employed in food protein analysis and conducts an extensive comparison to identify the most suitable method for various proteins. While these techniques offer distinct advantages for protein structure determination, the inherent complexity of food matrices presents ongoing challenges. Further research is necessary to develop and enhance more robust detection methods to improve accuracy in protein conformation and structure analysis.

Thermal Behavior of Pea and Egg White Protein Mixtures

The partial substitution of animal protein by plant protein is a new opportunity to produce sustainable food. Hence, to control the heat treatment of a composite protein ingredient, this work investigated the thermal behavior of mixtures of raw egg white (EW) and a laboratory-prepared pea protein isolate (PPI). Ten-percentage-by-weight protein suspensions prepared with different PPI/EW weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) at pH 7.5 and 9.0 were analyzed by differential scanning calorimetry (DSC) and dynamic rheology in temperature sweep mode (T < 100 °C). The DSC data revealed changes in the thermal denaturation temperatures (Td) of ovotransferrin, lysozyme, and pea legumin, supposing interactions between proteins. Denaturation enthalpy (∆H) showed a high pH dependence related to pea protein unfolding in alkaline conditions and solubility loss of some proteins in admixture. Upon temperature sweeps (25-95 °C), the elastic modulus (G') of the mixtures increased significantly with the EW content, indicating that the gel formation was governed by the EW protein. Two thermal sol-gel transitions were found in EW-containing systems. In particular, the first sol-gel transition shifted by approximately +2-3 °C at pH 9.0, probably by a steric hindering effect due to the presence of denatured and non-associated pea globulins at this pH.

Growing of fungi on the stored low denatured defatted soybean meals and the hydrolysis of proteins and isoflavone glycosides by fungal enzymes

Recently, more and more attention has been paid to the effects of fungal contamination and fungal enzymes secreted in raw grain on product quality. As the starting material of protein and active components, the quality of low denatured defatted soybean meals (LDSM) directly determines the qualities of subsequent products. In previous studies, we have revealed that infection with Aspergillus ochraceus protease causes significant hydrolysis of proteins. In this study, growing of fungi on the stored low denatured defatted soybean meals (LDSM) was analyzed by high-throughput sequencing and real-time PCR, which revealed that the abundance of Aspergillus increased significantly after storage. Twenty fungal proteases and 9 fungal glucosidases were found in stored LDSM and zymography showed that the proteases were of serine-type with some cysteine and aspartic activities. Proteolysis of the soybean storage proteins mainly occurred after the hydration of LDSM and the average molecular weight of soy proteins decreased from 57.9 kDa to 30.7 kDa after 60 min's of hydrolysis. Two-dimensional electrophoresis (2-DE) analysis found the polypeptide fragments from soybean 7S and 11S proteins with molecular weight around 10-25 kDa in the hydrated LDSM. Glycosylated isoflavones were hydrolyzed in both dry and hydrated stored LDSM which resulted in significant (p < 0.05) increase in the contents of isoflavone aglycones. This study suggested that fungi contamination be a new factor affecting the properties of LDSM derived soy protein products.

Forces involved in freeze-induced egg yolk gelation: Effects of various bond dissociation reagents on gel properties and protein structure changes

Urea, sodium dodecyl sulfate (SDS) and β-mercaptoethanol (2-ME) were used to monitor the roles of hydrogen bonds, hydrophobic interactions and disulfide bonds in frozen egg yolk. Yolk samples were prepared with a denaturant, and the textural characteristics, turbidity properties, protein patterns and structures were analysed. The results showed that SDS or 2-ME addition to egg yolk promoted its turbidity and texture properties, but urea changed the turbidity differently. SDS-PAGE results showed that yolk protein patterns with urea slightly reduced the amount of high molecular weight substances, whereas SDS and 2-ME addition increased the amount. ATR-FTIR spectroscopy revealed that the protein secondary structures changed from ordered structures to random coils. The texture properties were correlated with the protein secondary structure, especially β-sheets and β-turns. Thus, the three bond dissociation reagents induced protein denaturation. Hydrogen bonds were the critical force affecting frozen egg yolk gelation, followed by hydrophobic interactions and disulfide bonds.

Target identification of natural medicine with chemical proteomics approach: probe synthesis, target fishing and protein identification

Natural products are an important source of new drugs for the treatment of various diseases. However, developing natural product-based new medicines through random moiety modification is a lengthy and costly process, due in part to the difficulties associated with comprehensively understanding the mechanism of action and the side effects. Identifying the protein targets of natural products is an effective strategy, but most medicines interact with multiple protein targets, which complicate this process. In recent years, an increasing number of researchers have begun to screen the target proteins of natural products with chemical proteomics approaches, which can provide a more comprehensive array of the protein targets of active small molecules in an unbiased manner. Typically, chemical proteomics experiments for target identification consist of two key steps: (1) chemical probe design and synthesis and (2) target fishing and identification. In recent decades, five different types of chemical proteomic probes and their respective target fishing methods have been developed to screen targets of molecules with different structures, and a variety of protein identification approaches have been invented. Presently, we will classify these chemical proteomics approaches, the application scopes and characteristics of the different types of chemical probes, the different protein identification methods, and the advantages and disadvantages of these strategies.

Authentication of liquid egg composition using ATR-FTIR and NIR spectroscopy in combination with PCA

BACKGROUND

The starting point of this work is to propose a qualitative approach for authenticity confirmation of the composition of liquid egg products. To this end, it was aimed to detect the liquid egg authenticity and adulteration (with water) by using attenuated total reflectance Fourier-transform infrared (ATR-FTIR), near infrared (NIR) spectroscopy and chemometrics.

RESULTS

Liquid (n = 50) and dry (n = 50) samples of whole egg, egg yolk, egg white, and whole egg containing extra egg white (BXEW) and water (BXW) were prepared. Principal component analysis (PCA) models were formed using the data obtained from ATR-FTIR and NIR measurements of liquid and dry samples. A better classification was achieved with PCA model of ATR-FTIR measurements formed by using dry samples (100%) instead of liquid ones (80%). The best separation was obtained between dry sample groups of BXEW and BXW (adulterated). The presence of water content in liquid samples showed a negative effect on classification of the samples, while a good classification (100%) was obtained for NIR measurements of both liquid and dry sample groups. The developed PCA models achieved classification regardless of the form of egg samples (liquid or dry).

CONCLUSION

The results of the study revealed that adulterated egg samples (with water) could be qualitatively detected using ATR-FTIR and NIR spectroscopy techniques in combination with PCA. © 2019 Society of Chemical Industry.

Preparation, characterization and physicochemical properties of novel low-phosphorus egg yolk protein

BACKGROUND

In order to supply adequate dietary protein for chronic kidney disease (CKD) patients while simultaneously controlling phosphorus intake, a novel method was developed for the preparation of low-phosphorus egg yolk protein (LPYP) using alkaline protease auxiliary dephosphorization. In addition, the physicochemical properties of LPYP were studied.

RESULTS

In comparison with raw egg yolk protein (RYP) and defatted egg yolk protein (DFYP), LPYP was found to exhibit differences in amino acid (AA) composition, protein secondary structure, surface hydrophobicity, solubility and emulsion stability. It was observed that dephosphorization improved the AA composition, soluble protein content and dissolution stability of egg yolk protein. In addition, phosphate groups were found to impose a critical influence on the emulsion stability and particle size distribution. The final phosphorus to protein mass ratio (P/Pro) of LPYP was 5.64, which met the requirements of a protein diet for CKD patients. The FAO/WHO mode closeness and stability coefficient were 0.958 and 98.62% respectively.

CONCLUSION

LPYP can be effectively obtained by alkaline protease hydrolysis and subsequent alkali dephosphorization. The prepared LPYP can be considered to be a type of safe and suitable protein resource for CKD patients. © 2018 Society of Chemical Industry.

Hyphenated Analytical Methods in Determination of Biologically Active Compounds in Hen's Eggs

Hen's egg is a complete material needed for the development of the embryo; it is an important source of nutraceutical compounds, such as protein, fats, vitamins, trace metals, and minerals. Moreover, avian egg contains biologically active compounds that exhibit antibacterial and antimicrobial activities as well as antitumor, antiviral, antioxidant, immunomodulating, and therapeutic properties. Eggs are mostly very good sources of valuable, easily digestible proteins. This review focuses on the biologically active compounds from hen's egg and applications of these compounds in medicine and the pharmaceutical industry. Additionally, it gives an overview of the hyphenated separation techniques, including sample preparation, analysis, and identification, used in the proteomics and lipidomics analysis.

Direct matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis of lysozyme contained in hen egg white

As a natural antibacterial peptide, lysozyme (LZ) is widely used in medicine and the food industry. Despite many years of research on this compound, its new antibacterial properties are still to be determined. The primary aim of this work is to demonstrate the application of the matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometric analysis of LZ directly in hen egg white samples without extraction thereof. The egg white samples were kept over 10 weeks at room temperature and measured every week. The resulting positive and negative ion mass spectra were then compared to determine the intensity of the LZ mass peak. Storage of the egg white for over 10 weeks did not influence the LZ mass peak intensity (both positive and negative). It can be concluded that the LZ concentration in the egg white samples did not vary with time. The effect of the matrix/sample ratio on LZ detection was also examined, and it was found to be different in the case of positive and negative ionization. The mass peaks of LZ oligomeric forms were observed in all mass spectra, so the MALDI method could be used in subsequent studies.

Facile fabrication of egg white macroporous sponges for tissue regeneration

The availability of 3D sponges combining proper biochemical, biophysical, and biomechanical properties with enhanced capacity of in vivo engraftment and vascularization is crucial in regenerative medicine. A simple process is developed to generate macroporous scaffolds with a well-defined architecture of interconnected pores from chicken egg white (EW), a material with protein- and growth factor-binding features which has not yet been employed in regenerative medicine. The physicomechanical properties and degradation rates of the scaffold are finely tuned by using varying concentrations of the cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, without alteration of the biochemical traits. In vitro, EW scaffolds supported active metabolism, proliferation, and migration of human dermal fibroblasts, thereby generating uniform cellular constructs. In vivo, subcutaneous implantation in mice reveals negligible immune reaction and efficient cell and tissue ingrowth. Angiogenesis into EW scaffolds is enhanced as compared to standard collagen type I sponges used as reference material, likely due to significantly higher adsorption of the proangiogenic factor vascular endothelial growth factor. In summary, a material is presented derived by facile processing of a highly abundant natural product. Due to the efficient subcutaneous engraftment capacity, the sponges can find utilization for soft tissue regeneration.

Enrichment of phosphorylated peptides and proteins by selective precipitation methods

Protein phosphorylation is one of the most prominent post-translational modifications involved in the regulation of cellular processes. Fundamental understanding of biological processes requires appropriate bioanalytical methods for selectively enriching phosphorylated peptides and proteins. Most of the commonly applied enrichment approaches include chromatographic materials including Fe(3+)-immobilized metal-ion affinity chromatography or metal oxides. In the last years, the introduction of several non-chromatographic isolation technologies has increasingly attracted the interest of many scientists. Such approaches are based on the selective precipitation of phosphorylated peptides and proteins by applying various metal cations. The excellent performance of precipitation-based enrichment methods can be explained by the absence of any stationary phase, resin or sorbent, which usually leads to unspecific binding. This review provides an overview of recently published methods for the selective precipitation of phosphorylated peptides and proteins.

Identification of five reptile egg whites protein using MALDI-TOF mass spectrometry and LC/MS-MS analysis

Proteomics of egg white proteins of five reptile species, namely Siamese crocodile (Crocodylus siamensis), soft-shelled turtle (Trionyx sinensis taiwanese), red-eared slider turtle (Trachemys scripta elegans), hawksbill turtle (Eretmochelys imbricate) and green turtle (Chelonia mydas) were studied by 2D-PAGE using IPG strip pH 4-7 size 7 cm and IPG strip pH 3-10 size 24 cm. The protein spots in the egg white of the five reptile species were identified by MALDI-TOF mass spectrometry and LC/MS-MS analysis. Sequence comparison with the database revealed that reptile egg white contained at least seven protein groups, such as serpine, transferrin precursor/iron binding protein, lysozyme C, teneurin-2 (fragment), interferon-induced GTP-binding protein Mx, succinate dehydrogenase iron-sulfur subunit and olfactory receptor 46. This report confirms that transferrin precursor/iron binding protein is the major component in reptile egg white. In egg white of Siamese crocodile, twenty isoforms of transferrin precursor were found. Iron binding protein was found in four species of turtle. In egg white of soft-shelled turtle, ten isoforms of lysozyme were found. Apart from well-known reptile egg white constituents, this study identified some reptile egg white proteins, such as the teneurin-2 (fragment), the interferon-induced GTP-binding protein Mx, the olfactory receptor 46 and the succinate dehydrogenase iron-sulfur subunit.

Proteomics analysis of egg white proteins from different egg varieties

The market of specialty eggs, such as omega-3-enriched eggs, organic eggs, and free-range eggs, is continuously growing. The nutritional composition of egg yolk can be manipulated by feed diet; however, it is not known if there is any difference in the composition of egg white proteins among different egg varieties. The purpose of the study was to compare the egg white proteins among six different egg varieties using proteomics analysis. Egg white proteins were analyzed using two-dimensional gel electrophoresis (2-DE), and 89 protein spots were subjected to LC-MS/MS. A total of 23 proteins, belonging to Gallus gallus , were identified from 72 detected protein spots. A quiescence-specific protein precursor in egg white was identified for the first time in this study. Significant differences in the abundant levels of 19 proteins (from 65 protein spots) were observed among six egg varieties. Four proteins, ovalbumin-related protein Y, cystatin, avidin, and albumin precursor, were not different among these six egg varieties. These findings suggest that the abundance, but not the composition, of egg white proteins varied among the egg varieties.

Proteomic analysis of egg white proteins during storage

Egg storage causes egg white to lose its viscous nature to form a thin liquid, commonly referred to as egg white thinning. To understand the mechanisms underlying egg white thinning, white-shell eggs were used in the present study to determine the proteome-level changes of egg white proteins occurred during storage. Egg white thinning was observed visually after 20 days of storage at ambient temperature (22 ± 2 °C) when the maximum number of proteome-level changes occurred. The proteins that showed significant changes in abundance during storage included ovalbumin, clusterin, ovoinhibitor, ovotransferrin, and prostaglandin D2 synthase. Among these, only the abundance of clusterin was observed to change continuously during the storage period. Hence, it is expected that the increase in the concentrations of clusterin and ovoinhibitor along with the change of ovalbumin content during storage might contribute to egg white thinning. Degradation of ovalbumin/clusterin during egg storage may be due to the combined effect of proteolysis and increase in pH; this may also be partly responsible for egg white thinning phenomenon.

What makes an egg unique? Clues from evolutionary scenarios of egg-specific genes

The avian egg, which contains the egg yolk, the egg white, and the eggshell, represents the mostly advanced amniotic egg in oviparous vertebrates. In mammals, this reproductive strategy of laying egg has gradually evolved toward placentation. In order to better understand the unique status of the avian egg in the evolution of the vertebrate reproduction, we investigated the evolution of some Gallus gallus egg-specific protein-coding genes. Based on our finding and other recent research, we have summarized here that gene formation (such as ovalbumin genes, ovocalyxin-36 and apovitellenin-1 encoding genes in the G. gallus), gene divergence between G. gallus and mammals (such as the ovocalyxin-32 gene with its ortholog, the mammalian RARRES1, and the ovocleidin-116 with its ortholog, the mammalian MEPE), and gene loss (egg-expressed genes lost during the evolution of the mammals, such as vitellogenin and RBP encoding genes) play significant roles in the evolution of egg-specific genes.

Determination of holo- and apo-riboflavin binding protein in avian egg whites through circular dichroism and fluorescence spectroscopy

The hen egg white contains proteins able to strongly bind, with a definite stoichiometry, small molecules such as biotin and riboflavin, or ions such as Cu2+ or Fe3+. The complexation process modifies the spectral properties of these low-molecular-weight species. On the basis of these changes, it is possible, in principle, to measure the quantity of the binding protein and to evaluate the protein-substrate interactions. Here, we present a method to determine the concentration of both the apo and holo forms of the riboflavin-binding protein (RFBP) present in avian egg white, by measuring the circular dichroism (CD) related to the controlled addition of riboflavin (or vitamin B2) to the egg white. At the same time, front-face fluorescence is used to confirm the concentration of apo-RFBP obtained from CD data. The method is based on data only from spectroscopy, and no process involving either extraction, chromatography, electrophoresis, or mass spectrometry is involved. We study the egg whites from four different avian species, reporting and comparing the concentration of the apo- and holo-RFBP and the molar circular dichroism spectra (Deltaepsilon) of riboflavin in the RFBP binding site. Finally, egg whites from different hen individuals are analyzed, and a surprising variation of the RFBP concentration is found.

The chicken egg white proteome

Using 1-D PAGE and LC-MS/MS and MS(3) we identified 78 chicken egg white proteins, 54 of which were identified in egg white for the first time. All proteins were quantitated by calculating their exponentially modified protein abundance index (emPAI). Some previously known egg white components not characterized by amino acid sequences before, such as alpha-2-macroglobulin, were associated to a sequence for the first time. The predicted sequence was confirmed by MS-sequenced peptides covering 42% of the entire sequence. alpha-2-Macroglobulin occurred in egg white at the same concentration as ovostatin with which it showed 35% identity. For other proteins, which were previously only characterized by partial sequences, such as beta-ovomucin or ovalbumin X, we identified and confirmed predicted complete sequences with a high coverage by MS-sequenced peptides. New proteins included a 7 kDa protein consisting of a single secretoglobin sequence (ovosecretoglobin), a 7 kDa protein with similarity to black swan cygnin and turkey meleagrin (gallin) and proteins involved in binding, modification, and possibly detoxification, of bacterial lipopolysaccaride. The list of egg white proteins provided is by far the most comprehensive at present and is intended to serve as a starting point for the isolation and functional characterization of interesting new proteins.

Optimization of a pressurized liquid junction nanoelectrospray interface between CE and MS for reliable proteomic analysis

A pressurized liquid junction nanoelectrospray interface was designed and optimized for reliable on-line CE-MS coupling. The system was constructed as an integrated device for highly sensitive and selective analyses of proteins and peptides with the separation and spray capillaries fixed in a pressurized spray liquid reservoir equipped with the electrode for connection of the electrospray potential. The electrode chamber on the injection side of the separation capillary and the spray liquid reservoir were pneumatically connected by a Teflon tube filled with pressurized nitrogen. This arrangement provided precisely counterbalanced pressures at the inlet and outlet of the separation capillary. The pressure control system was driven by an electrically operated valve and maintained the optimum flow rate for the electrospray stability. All parts of the interface being in contact with the CEBGE, spray liquid and/or sample were made of glass or Teflon. The use of these materials minimized the electrospray chemical noise often caused by plastic softeners or material degradation. During optimization, the transfer of the separated zones between the separation and electrospray capillaries was monitored by UV absorbance and contactless conductivity detectors placed at the outlet of the separation capillary and inlet of the electrospray tip, respectively. This arrangement allowed independent monitoring of the effects of pressure, CE voltage and geometry of the liquid junction on the spreading and dilution of the separated zones after passage through the interface.

Competitive adsorption of proteins from total hen egg yolk during emulsification

In this article, the competitive adsorption of egg yolk proteins at oil/water interfaces during emulsification is studied. By using two-dimensional polyacrylamide electrophoresis and mass spectrometry, it was possible to characterize and identify adsorbing and non-adsorbing protein species. The egg yolk contains proteins with a wide range of molecular weights and pI. Lipoproteins adsorbed selectively throughout the pH range investigated. It is suggested that selectivity is determined by the average hydrophobic and hydrophilic domain lengths in the protein sequences where long average hydrophobic domain lengths result in high affinity for the interface and thus strong preferential adsorption.

Partial characterization of giant extracellular hemoglobin of Glossoscolex paulistus: A MALDI-TOF-MS study

In this work, MALDI-TOF-MS analysis was performed to obtain information on the molecular mass of the different subunits from the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy-form. Experiments were performed for the whole protein at pH 7.0, for the partially dissociated protein at pH 9.0, and for the fraction obtained from gel filtration in Sephadex G-200, at pH 9.0, corresponding to the isolated monomer d. Besides that, experiments were performed for the whole protein treated with 2-mercaptoethanol in order to monitor the effects of reduction of the disulfide bonds, which are expected to maintain the trimer (abc) in the native molecule. The results are compared to those reported for the homologous hemoglobin of Lumbricus terrestris (HbLt) and some tentative assignments are made for the observed polypeptides. The monomer d is found to exist in, at least, two major forms of identical proportions with masses of 16,355+/-25 and 16,428+/-24 Da, respectively. Two minor forms were also observed around 16 kDa for the monomers. Upon disulfide bonds reduction the peak associated to the trimer is absent in the mass spectrum, and new peaks assigned tentatively to the monomers a, b and c on the basis of comparison with Lumbricus terrestris hemoglobin literature data are observed. Their molecular masses were 18,258+/-30, 16,492+/-24 and 17,363+/-17 Da, respectively. Two linker chains for HbGp were also observed at 25,817+/-50 and 26,761+/-16 Da, and this result is different from HbLt, where four linker chains were reported in the range 24-32 kDa. Finally, trimers (abc) were observed at 51-52 kDa. This partial characterization, performed for the first time, is an important step in the characterization of subunits of this giant extracellular hemoglobin.