Lactoglobulin

β-Lactoglobulin is the major whey protein of cow and sheep's milk (~3 g/l), and is also present in many other mammalian species; a notable exception being humans. Its structure, properties and biological role have been reviewed many times.

Unlike the other main whey protein, α-lactalbumin, no clear function has been identified for β-lactoglobulin. β-lactoglobulin is a lipocalin protein, and can bind many hydrophobic molecules, suggesting a role in their transport. β-lactoglobulin has also been shown to be able to bind iron via siderophores and thus might have a role in combating pathogens. A homologue of β-lactoglobulin is lacking in human breast milk.

Several genetic variants have been identified, the main ones in the cow being labelled A and B. Because of its abundance and ease of purification, it has been subjected to a wide range of biophysical studies. Its structure has been determined several times by X-ray crystallography and NMR. One such structure is shown on the right (from http://www.pdb.org entry 3BLG). β-lactoglobulin is of direct interest to the food industry since its properties can variously be advantageous or disadvantageous in dairy products and processing

Bovine β-lactoglobulin is a relatively small protein of 162 residues, with an 18.4 kDa molecular weight (1 dalton being defined as 1 unified atomic mass unit). In physiological conditions it is predominantly dimeric, but dissociates to a monomer below about pH 3, preserving its native state as determined by using NMR. Conversely, β-lactoglobulin also occurs in tetrameric, octameric and other multimeric aggregation forms under a variety of natural conditions.

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