Ovalbumin

Ovalbumin is the main protein found in egg white, making up 60-65% of the total protein. Ovalbumin displays sequence and three-dimensional homology to the serpin superfamily, but unlike most serpins it is not a serine protease inhibitor. The function of ovalbumin is unknown, although it is presumed to be a storage protein.

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 (chicken egg ovalbumin is commonly used as a molecular weight marker for calibrating electrophoresis gels).


 * immunology (commonly used to stimulate an allergic reaction 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 acids, and its relative molecular mass is 45 kDa. It is a glycoprotein with 4 sites of glycosylation.

It is secreted from the cell. Unlike the signal sequences of most secreted proteins, Ovalbumin's signal sequence 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 prevents the absorption of the metals into the gastrointestinal tract and prevents poisoning.