Ovalbumin (abbreviatedOVA[1]) is the mainprotein found inegg white, making up approximately 55% of the total protein.[2] Ovalbumin displays sequence and three-dimensionalhomology to theserpin superfamily, but unlike most serpins it is not aserine protease inhibitor.[3] The function of ovalbumin is unknown, although it is presumed to be astorage protein.[4]
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 calibratingelectrophoresis gels).
The ovalbumin protein of chickens consists of 385amino acids, its relative molecular mass is42.7 kDa,[5] and it adopts aserpin-like structure.[6] Ovalbumin also has several modifications, includingN-terminal acetylation (G1),phosphorylation (S68, S344), and glycosylation (N292).[5] It has three isoforms, A1, A2, and A3, which vary based on the number of bound phosphate residues.[7] It is secreted from the cell, targeted by an internalsignal sequence (residues 21–47), rather than the N-terminal signal sequence commonly found in other secreted proteins. Ovalbumin'ssignal sequence is not cleaved off, but remains as part of the mature protein.[8]
When heated, ovalbumin undergoes aconformational change from its soluble, serpin structure into an insoluble all-β-sheet structure with exposedhydrophobic regions. This causes the protein to aggregate and cause the solidification associated with cooked egg white.[9]
