Proteomic analysis of hen egg white

A simple model for understanding the origin of the amide proton transfer MRI signal in tissue

Amide proton transfer (APT) imaging is a new molecular MRI technique that gives contrast at the cellular protein level. To better understand the origin of the APT signal in tissue, fresh and cooked hen eggs (n = 4) were imaged at 4.7 Tesla. The APT effect was quantified using the asymmetry in the magnetization transfer ratio (MTR(asym)) at the composite amide proton resonance frequency (3.5 ppm from the water resonance). The measured APT signals were significantly higher in the fresh egg white (20.1% ± 0.9%) than in the fresh egg yolk (-1.4% ± 1.1%; P < 0.001), and in the cooked egg white (2.8% ± 0.7%; P < 0.001), all of which have similar absolute protein contents. The data support the notion that the APT effect observed in vivo is associated with mobile proteins in tissue, such as those in the cytoplasm.

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.

Antimicrobial potential of egg yolk ovoinhibitor, a multidomain Kazal-like inhibitor of chicken egg

Chicken egg ovoinhibitor is a multidomain Kazal-type serine protease inhibitor with unknown function. Comparison of expression between different tissues indicated that ovoinhibitor is highly expressed in the magnum and liver followed by the uterus, which secrete egg white, egg yolk, and eggshell precursors, respectively. The results also revealed that ovoinhibitor expression is increased in the liver during sexual maturation followed by a subsequent decrease in mature hens. Ovoinhibitor was purified from the egg yolk plasma from nonfertilized eggs using two consecutive affinity chromatographies and gel filtration. Purified egg yolk ovoinhibitor was shown to inhibit trypsin and subtilisin. It was shown that purified egg yolk ovoinhibitor exhibited antimicrobial activities against Bacillus thuringiensis . The results suggest that this anti-protease plays a significant role in antibacterial egg defense against Bacillus spp., preventing contamination of table eggs (nonfertilized eggs) and protecting the chick embryo (fertilized eggs).

Ovocalyxin-36 and other LBP/BPI/PLUNC-like proteins as molecular actors of the mechanisms of the avian egg natural defences

The chicken egg possesses physical and chemical barriers to protect the embryo from pathogens. OCX-36 (ovocalyxin-36) was suggested to be a 36 kDa eggshell-specific protein that is secreted by the regions of the oviduct responsible for eggshell formation. Its expression is strongly up-regulated during shell calcification. This protein was also detected in vitelline membrane and expressed in gut tissues. Analysis of the OCX-36 protein sequence revealed that OCX-36 is related to the BPI (bactericidal permeability-increasing proteins)/LBP [LPS (lipopolysaccharide)-binding proteins]/PLUNC (palate, lung and nasal epithelium clone) superfamily, and that there are strong similarities between the exon/intron organization of the mammalian LBP/BPI and the avian OCX-36 genes. A recent study revealed that OCX-36 originates from a tandem duplication of an ancestral BPI/LBP/PLUNC gene, after the divergence of birds and mammals. Its antimicrobial activity was recently investigated and it was shown that OCX-36 binds to LPS from Escherichia coli. High-throughput methodologies have led to the identification of approximately 1000 new egg proteins. Among these are LBP/BPI proteins that might play a role in the natural defences of the egg to protect the embryo during its development in the external milieu, and may function to keep the table egg free of pathogens. The function of these BPI-like molecules is the subject of intense research to characterize their putative LPS-binding properties and antimicrobial activity.

Analysis of peptides and proteins using sub-2 μm fully porous and sub 3-μm shell particles

The objective of this study was to evaluate the potential of sub-2 μm totally porous particles and sub-3 μm shell particles for peptide and protein analysis. Specific analytical strategies must be developed for these biomolecules as their importance in the pharmaceutical industry increases and as their structural complexity involves some issues when classical LC conditions are employed. Attention was paid on comparing these different columns in various LC conditions (different temperatures, gradient times, and mobile phase flow rates). The comparison of the different supports was assessed considering columns characteristics (quality of packing, silanol activity, pore size, totally porous or shell particles). In this article, peptides were first analyzed with both column technologies. Similar results to those achieved with low molecular weight compounds were obtained (peak capacity >100 for t(grad) around 3 min and columns dimensions of 2.1 mm id × 50 mm), but specific conditions were required (elevated temperature and the use of a volatile ion-pairing reagent, namely TFA). For peptide analysis following tryptic digestion, the goal was to improve peak capacity and resolution because of the large number of generated peptides. For this purpose, longer columns packed with porous sub-2 μm or shell sub-3 μm particles (i.e., 150 mm) and gradient times (i.e., up to 30 min) were tested. On the other hand, proteins in their intact forms have higher molecular weights (MW>5000 Da) and a tertiary structure, thus requiring different conditions in terms of stationary phase hydrophobicity (C(4)vs. C(18)) and pore size (300 vs. 120 Å). In addition, there were issues with adsorption onto the LC system and/or the column itself. This study showed that proteins with MWs lower than 40,000 Da required chromatographic conditions close to those employed for peptide analysis. For larger proteins, a C(4) 300 Å stationary phase gave the best results, confirming theoretical predictions.

Lysozyme as a barrier to growth of Bacillus anthracis strain Sterne in liquid egg white, milk and beef

In this study, we investigated the role of lysozyme on the viability of Bacillus cereus, Bacillus subtilis, Bacillus pumilus and Bacillus anthracis (Sterne) in egg white (EW), ground beef and milk. At 35 °C in EW, growth rates (GR) for B. cereus, B. subtilis, B. pumilus and B. anthracis were 0.005, -0.018, -0.028 and -0.029 OD(600)/h, respectively. Heat-treating EW at 55 and 60 °C reduced the inactivating effect of EW by 3.1 and 10.5-fold, respectively. Addition of lysozyme (2 mg/ml) to 60 °C-treated EW increased the inactivation rate 5.76-fold, indicating involvement of lysozyme in B. anthracis inactivation. B. anthracis inactivation was influenced by pH, as shown by a progressive increase in inactivation rate from 0.25 to -4.42 logs CFU/h over a pH range of 6.0-8.5. Adding 2 mg/ml lysozyme to milk and ground beef also suppressed the growth of B. anthracis 3.3 and 6.5-fold, respectively. These data indicate that lysozyme, as a natural component of EW or potential additive in other foods, could reduce biothreat risks presented by bioterror agents.

Identification and characterisation of the BPI/LBP/PLUNC-like gene repertoire in chickens reveals the absence of a LBP gene

Palate, lung and nasal epithelial clone (PLUNC) proteins are structural homologues to the innate defence molecules LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI). PLUNCs make up the largest portion of the wider BPI/LBP/PLUNC-like protein family and are amongst the most rapidly evolving mammalian genes. In this study we systematically identified and characterised BPI/LBP/PLUNC-like protein-encoding genes in the chicken genome. We identified eleven complete genes (and a pseudogene). Five of them are clustered on a >50 kb locus on chromosome 20, immediately adjacent to BPI. In addition to BPI, we have identified presumptive orthologues LPLUNCs 2, 3, 4 and 6, and BPIL-2. We find no evidence for the existence of single domain containing proteins in birds. Strikingly our analysis also suggests that there is no LBP orthologue in chicken. This observation may in part account for the relative resistance to LPS toxicity observed in birds. Our results indicate significant differences between the avian and mammalian repertoires of BPI/LBP/PLUNC-like genes at the genomic and transcriptional levels and provide a framework for further functional analyses of this gene family in chickens.

In-depth analysis of the chicken egg white proteome using an LTQ Orbitrap Velos

Background

Hen's egg white has been the subject of intensive chemical, biochemical and food technological research for many decades, because of its importance in human nutrition, its importance as a source of easily accessible model proteins, and its potential use in biotechnological processes. Recently the arsenal of tools used to study the protein components of egg white has been complemented by mass spectrometry-based proteomic technologies. Application of these fast and sensitive methods has already enabled the identification of a large number of new egg white proteins. Recent technological advances may be expected to further expand the egg white protein inventory.

Results

Using a dual pressure linear ion trap Orbitrap instrument, the LTQ Orbitrap Velos, in conjunction with data analysis in the MaxQuant software package, we identified 158 proteins in chicken egg white with two or more sequence unique peptides. This group of proteins identified with very high confidence included 79 proteins identified in egg white for the first time. In addition, 44 proteins were identified tentatively.

Conclusions

Our results, apart from identifying many new egg white components, indicate that current mass spectrometry technology is sufficiently advanced to permit direct identification of minor components of proteomes dominated by a few major proteins without resorting to indirect techniques, such as chromatographic depletion or peptide library binding, which change the composition of the proteome.

Liquid chromatography and mass spectrometry in food allergen detection

Food allergy is an important issue in the field of food safety because of the hazards for affected persons and the hygiene requirements and legal regulations imposed on the food industry. Consumer protection and law enforcement require suitable analytical techniques for the detection of allergens in foods. Immunological methods are currently preferred; however, confirmatory alternatives are needed. The determination of allergenic proteins by liquid chromatography and mass spectrometry has greatly advanced in recent years, and gel-free allergenomics is becoming a routinely used approach for the identification and quantitation of food allergens. The present review provides a brief overview of the principles of proteomic procedures, various chromatographic set ups, and mass spectrometry instrumentation used in allergenomics. A compendium of published liquid chromatography methods, proteomic analyses, typical marker peptides, and quantitative assays for 14 main allergy-causing foods is also included.

Succinimidyl residue formation in hen egg-white lysozyme favors the formation of intermolecular covalent bonds without affecting its tertiary structure

Protein chemical degradations occur naturally into living cells as soon as proteins have been synthesized. Among these modifications, deamidation of asparagine or glutamine residues has been extensively studied, whereas the intermediate state, a succinimide derivative, was poorly investigated because of the difficulty of isolating those transient species. We used an indirect method, a limited thermal treatment in the dry state at acidic pH, to produce stable cyclic imide residues in hen lysozyme molecules, enabling us to examine the structural and functional properties of so modified proteins. Five cyclic imide rings have been located at sites directly accessible to solvent and did not lead to any changes in secondary or tertiary structures. However, they altered the catalytic properties of lysozyme and significantly decreased the intrinsic stability of the molecules. Moreover, dimerization occurred during the treatment, and this phenomenon was proportional to the extent of chemical degradation. We propose that succinimide formation could be responsible for covalent bond formation under specific physicochemical conditions that could be found in vivo.

Primary structure of potential allergenic proteins in emu (Dromaius novaehollandiae) egg white

The emu (Dromaius novaehollandiae) egg is considered promising as an alternative egg product. To obtain basic biochemical information on emu egg white, the major protein compositions in emu and chicken egg whites and the primary structures of potential allergenic proteins were compared. The dominant protein in emu egg white was ovotransferrin (OVT), followed by ovalbumin (OVA) and TENP protein. The OVA and ovomucoid (OVM) levels in emu egg white were estimated as significantly lower than those in chicken egg white by Western blotting and enzyme-linked immunosorbent assays using anti-chicken OVA or OVM antibodies. Lysozyme and its enzymatic activity were not detected in emu egg white. OVT, OVA, and OVM genes were also cloned, and their nucleotide and amino acid sequences were determined. The protein sequences of OVT, OVA, and OVM from emu showed lower similarities to those of chicken than other avian species, such as quail and turkey. These results emphasize the low allergenicity of emu egg white and its potential as an alternative to chicken egg white.

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.

Lipocalin-type prostaglandin D synthase and egg white cystatin react with IgE antibodies from children with egg allergy

BACKGROUND

Ovalbumin, ovomucoid, ovotransferrin, lysozyme, and ovomucin are known to be major allergens found in egg white. Egg white protein is composed of over 30 proteins; many of which have neither been identified nor their allergenicities characterized. This study set out to analyze whether unknown proteins that bind to IgE antibodies in serum from patients with egg allergy exist in egg white.

METHODS

Diluted egg white proteins were separated by 2-dimensional (2-D) gel electrophoresis. Immunolabeling was performed on individual patient sera from 19 child patients with egg white allergy and 11 negative control subjects. Spots of egg white proteins that bound to the patients' IgE were identified by mass spectrometry-based proteomics.

RESULTS

Egg white proteins were separated into 63 spots. Twenty-five of the 63 reacted with egg allergy patients' sera, and 10 of the 25 reactive spots showed IgE-reactivity to controls as well. Specific bindings to the IgE from egg allergy patients were found in 15 spots; one of which was confirmed as ovotransferrin. Among the other 14 protein spots, egg white cystatin and lipocalin-type prostaglandin D synthase (L-PGDS) were newly identified proteins that reacted with IgE in patients with egg allergy.

CONCLUSIONS

We demonstrated that L-PGDS and cystatin reacted with serum IgE in patients with egg allergy. Our proteomics-based analysis in egg white gives a comprehensive map of proteins bound with IgE and should assist in enabling more accurate diagnoses and recommendations of desensitizing treatments for individual patients.

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.

Mechanisms of egg contamination by Salmonella Enteritidis

Salmonella Enteritidis (SE) has been the major cause of the food-borne salmonellosis pandemic in humans over the last 20 years, during which contaminated hen's eggs were the most important vehicle of the infection. Eggs can be contaminated on the outer shell surface and internally. Internal contamination can be the result of penetration through the eggshell or by direct contamination of egg contents before oviposition, originating from infection of the reproductive organs. Once inside the egg, the bacteria need to cope with antimicrobial factors in the albumen and vitelline membrane before migration to the yolk can occur. It would seem that serotype Enteritidis has intrinsic characteristics that allow an epidemiological association with hen eggs that are still undefined. There are indications that SE survives the attacks with the help of antimicrobial molecules during the formation of the egg in the hen's oviduct and inside the egg. This appears to require a unique combination of genes encoding for improved cell wall protection and repairing cellular and molecular damage, among others.

Chicken egg yolk cytoplasmic proteome, mined via combinatorial peptide ligand libraries

The use of combinatorial peptide ligand libraries (CPLLs), containing hexapeptides terminating with a primary amine, or modified with a terminal carboxyl group, or with a terminal tertiary amine, allowed discovering and identifying a large number of previously unreported egg yolk proteins. Whereas the most comprehensive list up to date [K. Mann, M. Mann, Proteomics, 8 (2008) 178-191] tabulated about 115 unique gene products in the yolk plasma, our findings have more than doubled this value to 255 unique protein species. From the initial non-treated egg yolk it was possible to find 49 protein species; the difference was generated thanks to the use of the three combined CPLLs. The aberrant behaviour of some proteins, upon treatment via the CPLL method, such as proteins that do not interact with the library, is discussed and evaluated. Simplified elution protocols from the CPLL beads are taken into consideration, of which direct elution in a single step via sodium dodecyl sulphate desorption seems to be quite promising. Alternative methods are suggested. The list of egg yolk components here reported is by far the most comprehensive at present and could serve as a starting point for isolation and functional characterization of proteins possibly having novel pharmaceutical and biomedical applications.

Identification and characterization of the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) in hen egg

Using zymography and mass spectrometry, we identified for the first time the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) as a complex with TIMP-2 (tissue inhibitor of metalloproteinases) in egg white and yolk. Real-time polymerase chain reaction confirmed that MMP-2 and its inhibitors TIMP-2 and TIMP-3 were expressed all along the oviduct and in the liver of laying hens. We also demonstrated that the processing of pro-MMP-2 into mature MMP-2 by serine proteases does not occur in vivo, although purified pro-MMP-2 undergoes proteolytic maturation by these proteases in vitro. Moreover, the relative pro-MMP-2 activity assessed by gelatin zymography was shown to decrease in egg white during the storage of unfertilized or fertilized eggs. However, the mature form of 62 kDa MMP-2 could not be detected. The fact that MMP-2 is found as a proform in fresh eggs suggests that the activity of this metalloprotease is regulated under specific conditions during embryonic development.

Novel egg white–based 3-D cell culture system

Although three dimensional (3-D) cell culture systems have numerous advantages over traditional monolayer culture, the currently available 3-D cell culture media are cost-prohibitive for regular use by the majority of research laboratories. Here we show a simple system based on avian egg white that supports growth of cells in 3-D, at a significantly decreased cost. Specifically, we show that growth of immortalized human breast epithelial cells (MCF10A) in egg white–based medium results in formation of acini with hollow lumens, apoptotic clearance of the cells in the lumen, and apicobasal polarization comparable to what has been described using established 3-D culture media such as reconstituted basement membrane preparations (BM). There was no significant difference in MCF10A proliferation and acinar size between egg white and BM. We also cultured different established cell lines, oncogene-transformed MCF10A, and mouse mammary epithelial cells in egg white and BM, and observed similar morphology. In summary, our data convincingly argue that egg white can be used as a suitable alternative model for 3-D cell culture studies. We strongly believe that this simple and inexpensive method should allow researchers to perform 3-D cell culture experiments on a regular basis, and result in a dramatic increase of use of the 3-D cell culture in research. Thus, this finding lays the foundation for significantly increased, cost-effective use of 3-D cultures in cell biology.

New insights into the structure of apolipoprotein B from low-density lipoproteins and identification of a novel YGP-like protein in hen egg yolk

Apoproteins of low-density lipoproteins (LDL) and soluble proteins (livetins) contained in hen egg yolk plasma have been demonstrated as being essential to the interfacial and emulsifying properties of yolk. The knowledge of their structure is necessary to better understand these properties. Purified protein fractions were separated by SDS-PAGE or 2D-PAGE and identified through the LC-MS/MS of their trypsin peptides. Hen blood apolipoprotein B gives rise to nine different apoproteins in LDL after maturation and proteolysis. Among these apoproteins, two protein fragments appeared to be less accessible to proteases and could be enriched in beta-sheets and firmly associated with lipids. Plasma soluble proteins were constituted by approximately 45% of yolk immunoglobulins with a high heterogeneity of the variable regions of both heavy and light chains, 41% of glycoproteins constituted by YGP42 and YGP40, 14% of albumins, and one new minor protein we called YGP30, showing 75% similarity to YGP40.

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.

Using Proteomics to Understand Avian Systems Biology and Infectious Disease

The proteome is defined as the protein complement to the genome. Proteomics is the study of the proteome. Several techniques are frequently used in proteomics; these include 2-hybrid systems, 2-dimensional gel electrophoresis, and mass spectrometry. Systems biology is a scientific approach that takes into account the complex relationships among and between genes and proteins and determines how all of these interactions come together to form a functional organism. Proteomic tools can simultaneously probe the properties of numerous proteins and thus are a great aid to the emerging field of systems biology, in which the functional interactions of numerous proteins are studied instead of studying individual proteins as isolated entities. In the field of avian biology, proteomics has been used to study everything from the development and function of organs and systems to the interactions of infectious agents and the altered states that they induce in their hosts.

Cloning of Ovocalyxin-36, a Novel Chicken Eggshell Protein Related to Lipopolysaccharide-binding Proteins, Bactericidal Permeability-increasing Proteins, and Plunc Family Proteins

The avian eggshell is a composite biomaterial composed of noncalcifying eggshell membranes and the overlying calcified shell matrix. The shell is deposited in a uterine fluid where the concentration of different protein species varies at different stages of its formation. The role of avian eggshell proteins during shell formation remains poorly understood, and we have sought to identify and characterize the individual components in order to gain insight into their function during elaboration of the eggshell. In this study, we have used direct sequencing, immunochemistry, expression screening, and EST data base mining to clone and characterize a 1995-bp full-length cDNA sequence corresponding to a novel chicken eggshell protein that we have named Ovocalyxin-36 (OCX-36). Ovocalyxin-36 protein was only detected in the regions of the oviduct where egg-shell formation takes place; uterine OCX-36 message was strongly up-regulated during eggshell calcification. OCX-36 localized to the calcified eggshell predominantly in the inner part of the shell, and to the shell membranes. BlastN data base searching indicates that there is no mammalian version of OCX-36; however, the protein sequence is 20-25% homologous to proteins associated with the innate immune response as follows: lipopolysaccharide-binding proteins, bactericidal permeability-increasing proteins, and Plunc family proteins. Moreover, the genomic organization of these proteins and OCX-36 appears to be highly conserved. These observations suggest that OCX-36 is a novel and specific chicken eggshell protein related to the superfamily of lipopolysaccharide-binding proteins/bactericidal permeability-increasing proteins and Plunc proteins. OCX-36 may therefore participate in natural defense mechanisms that keep the egg free of pathogens.