Ovalbumin is the main protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 found in egg white

Egg white

Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...

, making up 60-65% of the total protein. Ovalbumin displays sequence and three-dimensional homology

Homology (chemistry)

In chemistry, homology refers to the appearance of homologues. A homologue is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene group, a peptide residue, etcetera....

 to the serpin

Serpin

Serpins are a group of proteins with similar structures that were first identified as a set of proteins able to inhibit proteases. The acronym serpin was originally coined because many serpins inhibit chymotrypsin-like serine proteases .The first members of the serpin superfamily to be extensively...

 superfamily, but unlike most serpins it is not a serine protease

Serine protease

Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the active site.They are found ubiquitously in both eukaryotes and prokaryotes...

 inhibitor. The function of ovalbumin is unknown, although it is presumed to be a storage protein

Storage protein

Storage proteins are biological reserves of metal ions and amino acids, used by organisms. They are found in plant seeds, egg whites, and milk....

.

Research

Ovalbumin is an important protein in several different areas of research, including:

• general studies of protein structure and properties (because it is available in large quantities).

• studies of serpin structure and function (the fact that ovalbumin does not inhibit proteases means that by comparing its structure with that of inhibitory serpins, the structural characteristics required for inhibition can be determined).

• proteomics
  Proteomics
  Proteomics is the large-scale study of proteins, particularly their structures and functions. Proteins are vital parts of living organisms, as they are the main components of the physiological metabolic pathways of cells. The term "proteomics" was first coined in 1997 to make an analogy with...
  
   (chicken egg ovalbumin is commonly used as a molecular weight marker for calibrating electrophoresis
  Electrophoresis
  Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...
  
   gels).

• immunology
  Immunology
  Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders ; the...
  
   (commonly used to stimulate an allergic reaction
  Allergy
  An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
  
   in test subjects, e.g. established model allergen for airway hyper-responsiveness AHR).

(For in-vivo and in-vitro studies based on ovalbumin it is important that the endotoxin content is less than 1 EU/mg.)

Structure

The ovalbumin protein of chickens is made up of 385 amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s, and its relative molecular mass is 45 kDa. It is a glycoprotein

Glycoprotein

Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

 with 4 sites of glycosylation.

It is secreted from the cell. Unlike the signal sequences of most secreted proteins, Ovalbumin's signal sequence

Signal peptide

A signal peptide is a short peptide chain that directs the transport of a protein.Signal peptides may also be called targeting signals, signal sequences, transit peptides, or localization signals....

 is not cleaved. Additionally it is not located directly on the N-terminus, but rather internally, starting at residue 21 and ending at residue 47.

Medicinal characteristics

In cases where poisoning by heavy metals (such as Iron) is suspected, ovalbumin may be administered. Ovalbumin chelates to heavy metals and traps the metal ions within the sulfhydryl bonds of the protein. Chelating

Chelation

Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....

prevents the absorption of the metals into the gastrointestinal tract and prevents poisoning.