Egg White and Yolk Protein Atlas: New Protein Insights of a Global Landmark Food

Abstract

(1) Background: The chicken egg is an animal product of great agronomic interest. The egg white and yolk constitute high-quality protein sources for humans with high digestibility and well-balanced amino acid profiles. Despite the egg white and yolk protein's undisputed value, research to unravel their full proteome content and its properties is still ongoing. We aimed to exhaustively analyze the proteome of egg white and yolk by applying intrinsic proteomics and bioinformatics approaches in order to unravel the full protein potential of this landmark food. (2) Methods: A total of 45 freshly laid, unfertilized, chicken eggs were subjected to nanoLC-MS/MS Orbitrap analysis following a peptide pre-fractionation step. A comprehensive bioinformatics processing step was undertaken towards elucidating potential activities and roles of identified molecules. In parallel, the literature was mined concerning all reported egg white and yolk protein identifications. (3) Results: Our analysis revealed 371 and 428 new proteins, reported for the first time to be present in the egg white and yolk, respectively. From the bioactivity standpoint, egg white and yolk proteins showed high enrichment for antioxidant and anti-inflammatory processes, while exerting high relevance for the apoptosis and focal adhesion pathways. (4) Conclusions: Egg white and yolk proteins exert diverse and multifaceted properties. A total of 799 proteins were reported for the first time as being part of the egg and yolk. Our novel protein data enriched those already published in the literature and the first ever chicken egg white and yolk Protein Atlas, comprising 1392 protein entries, was generated. This dataset will provide a cornerstone reference for future studies involving egg proteins.

Keywords: chicken; egg; egg white; egg yolk; proteins; proteomics.

Figure 1

Timeline of proteomics data published across the years concerning egg white (A) and egg yolk (B) protein identifications. X axis: year of article publication. Y axis: number of protein identifications. * Indicates studies that used both reviewed & unreviewed protein datasets from the UniProt database. ** The present study used reviewed datasets of proteins from UniProt for MS/SM spectral identifications [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31].

Figure 1

Timeline of proteomics data published across the years concerning egg white (A) and egg yolk (B) protein identifications. X axis: year of article publication. Y axis: number of protein identifications. * Indicates studies that used both reviewed & unreviewed protein datasets from the UniProt database. ** The present study used reviewed datasets of proteins from UniProt for MS/SM spectral identifications [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31].

Figure 2

Grouping of proteins present in (A) egg white, (B) egg yolk according to their bioactivity. Molecules were assigned to five categories: antioxidant, antimicrobial, antihypertensive, anti-inflammatory, immunomodulatory. Protein names in black correspond to molecules reported by previous studies also identified by the present study. Protein names in red depict newly reported entries identified for the first time in the corresponding egg domains by the present study.

Figure 3

Overview of proteins present in the egg white and egg yolk categorized according to their molecular function. Protein names in black correspond to molecules reported by previous studies also identified by the present study. Protein names in red are newly reported entries identified for the first time in the corresponding egg domains by the present study.

Figure 4

Gene Ontology (GO) annotation of the sum of egg white proteins available from all studies (including the present study) according to (A) biological process, (B) molecular function and (C) cellular component.

Figure 5

Gene Ontology (GO) annotation of the sum of egg yolk proteins available from all studies (including the present study) according to (A) biological process, (B) molecular function and (C) cellular component.

Figure 6

(A) KEGG pathway enrichment analysis for all identified proteins in egg white. The X— axis shows KEGG pathways significantly enriched for the identified proteins and the Y— axis shows the enrichment scores of these items. (B) Pathway map for identified proteins and their positioning in the apoptosis pathway. Solid line connects two pathway nodes if a path between them exists in the KEGG database. Dotted line indicates an inferred path from an input sequence or a query node to a known pathway.

Figure 7

(A) KEGG pathway enrichment analysis for all identified proteins in egg yolk. The X—axis shows KEGG pathways significantly enriched for the identified proteins and the Y—axis shows the enrichment scores of these items. (B) Pathway map for identified proteins and their positioning in the focal adhesion pathway. Solid lines connect two pathway nodes if a path between them exists in the KEGG database. Dotted line indicates an inferred path from an input sequence or a query node to a known pathway.

Figure 8

Egg white and egg yolk Protein Atlas. A total of 1392 unique proteins are present in the egg white and egg yolk. The figure presents data including identifications from all previously published articles as well as proteins reported in the present study. A Venn diagram is used to show that 579 proteins are uniquely present in the egg white, 584 proteins are characteristic for the egg yolk and 229 are commonly present in the egg white and egg yolk.