Casein Beta (CSN2)

The caseins have been shown to be members of a multigene family in at least 2 species, cow and man. They are among the most rapidly diverging groups of proteins. Bovine milk contains 4 caseins, 2 alpha, 1 beta, and 1 kappa . Human milk, on the other hand, contains only 2 caseins, beta and kappa. Beta-casein is the major casein in human milk, accounting for as much as 30% of its total protein mass. In addition to being the primary source of essential amino acids, beta-casein, in concert with kappa-casein, forms micelles that transport calcium and phosphorus to the developing infant. The N-terminal phosphoserine/phosphothreonine amino acids of beta-casein are crucial to the biologic function of the molecule, and variations in their number could affect the overall quality of milk.