Ovalbumin (abbreviated OVA) is the main
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
found in
egg white, making up approximately 55% of the total protein.
Ovalbumin displays sequence and three-dimensional
homology to the
serpin
Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be id ...
superfamily, but unlike most serpins it is not a
serine protease
Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site.
They are found ubiquitously in both eukaryotes and prokaryotes. Seri ...
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
Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see the ...
(commonly used to stimulate an
allergic reaction
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...
in test subjects; e.g., established model allergen for
airway hyper-responsiveness Bronchial hyperresponsiveness (or other combinations with airway or hyperreactivity, BH used as a general abbreviation) is a state characterised by easily triggered bronchospasm (contraction of the bronchioles or small airways).
Bronchial hyperresp ...
, 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 consists of 385
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, its relative molecular mass is 42.7
kDa
The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at re ...
,
[
] and it adopts a
serpin
Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be id ...
-like structure. Ovalbumin also has several modifications, including N-terminal acetylation (G1), phosphorylation (S68, S344), and glycosylation (N292).
It is secreted from the cell, targeted by an internal
signal sequence (residues 21–47), rather than the N-terminal signal sequence commonly found in other secreted proteins. Ovalbumin's
signal sequence is not cleaved off, but remains as part of the mature protein.
Change upon heating
When heated, ovalbumin undergoes a
conformational change from its soluble, serpin structure into an insoluble all-
β-sheet
The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a g ...
structure with exposed
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, t ...
regions. This causes the protein to aggregate and cause the solidification associated with cooked egg white.
See also
*
Egg allergy
Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaph ...
References
External links
*
{{Albumins
Storage proteins
Avian proteins