Ovalbumin

Structure of ovalbumin (PDB: 1OVA​)

Ovalbumin (abbreviated OVA^[1]) is the main protein found in egg white, making up 60-65% of the total protein.^[2] Ovalbumin displays sequence and three-dimensional homology to the serpin superfamily, but unlike most serpins it is not a serine protease inhibitor.^[3] The function of ovalbumin is unknown, although it is presumed to be a storage protein.^[4]

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 consists of 385 amino acids, its relative molecular mass is 45 kDa,^[5] and it adopts a serpin-like structure.^[6] Ovalbumin also has several modifications, including N-terminal acetylation (G1), phosphorylation (S68, S344), and glycosylation (N292).^[5] 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.^[7]

Change upon heating

When heated, ovalbumin undergoes a conformational change from its soluble, serpin structure into an insoluble all-β-sheet structure with exposed hydrophobic regions. This causes the protein to aggregate and cause the solidification associated with cooked egg white.^[8]

Medicinal characteristics

In cases where poisoning by heavy metals (such as Iron) is suspected, ovalbumin may be administered.^[9] 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.

See also

• Egg allergy

References

1. ↑ Sano Kunio; Kanna Haneda; Gen Tamura; Kunio Shirato (1999). "Ovalbumin (OVA) and Mycobacterium tuberculosis Bacilli Cooperatively Polarize Anti-OVA T-helper (Th) Cells toward a Th1-Dominant Phenotype and Ameliorate Murine Tracheal Eosinophilia". Am. J. Respir. Cell Mol. Biol. 20 (6): 1260–1267. doi:10.1165/ajrcmb.20.6.3546. Retrieved 28 December 2011. 
2. ↑ Huntington JA; Stein PE (2001). "Structure and properties of ovalbumin.". Journal of Chromatography B 756 (1-2): 189–198. doi:10.1016/S0378-4347(01)00108-6. PMID 11419711. 
3. ↑ Hu H.Y., Du H.N. (2000). "Alpha to Beta Structural Transformation of Ovalbumin: Heat and pH Effects". Journal of Protein Chemistry 19 (3): 177–183. doi:10.1023/A:1007099502179. PMID 10981809. 
4. ↑ Gettins PGW (2002) Serpin structure, mechanism, and function. Chemical Reviews 102(12): 4751-4804.
5. 1 2 Nisbet AD, Saundry RH, Moir AJG, Fothergill LA, Fothergill JE (1981) The complete amino-acid sequence of hen ovalbumin. European Journal of Biochemistry 115(2): 335.
6. ↑ Stein, Penelope E.; Leslie, Andrew G. W.; Finch, John T.; Carrell, Robin W. (1991-10-05). "Crystal structure of uncleaved ovalbumin at 1·95 Å resolution". Journal of Molecular Biology 221 (3): 941–959. doi:10.1016/0022-2836(91)80185-W. 
7. ↑ Robinson A, Meredith C, Austen BM (1986) Isolation and properties of the signal region from ovalbumin. FEBS Letters 203(2): 243-246.
8. ↑ Hu, H. Y.; Du, H. N. (2000-04-01). "α-to-β Structural Transformation of Ovalbumin: Heat and pH Effects". Journal of Protein Chemistry 19 (3): 177–183. doi:10.1023/A:1007099502179. ISSN 0277-8033. 
9. ↑ Dominiczak M, Baynes J, Medical Biochemistry, 2d edition (2004), p59.

External links

• Ovalbumin at the US National Library of Medicine Medical Subject Headings (MeSH)