Posttranslational modifications of caseins

The caseins exhibit a high degree of heterogeneity as a result of posttranslational modifications (PTMs). Phosphorylation of the αs1-, αs2-, and β-caseins and glycosylation of κ-casein are the best-known modifications and are critical for the formation and stability of casein micelles. κ-Casein, in particular, has long been known to exhibit a high degree of variability in glycosylation, specifically in the caseinomacropeptide region, which is responsible for the stabilization of the micelle. It is somewhat surprising to see so much variability in such important structural features. In recent years, the adoption of proteomic techniques has greatly enhanced our ability to unravel heterogeneity in proteins arising from complex and variable patterns of PTMs. In this chapter, a summary of our knowledge of the PTMs of caseins in bovine milk is attempted, with a particular emphasis on κ-casein and the implications that variations in PTMs have for dairy processors. As increasing attention is also being paid to PTMs in milks from other species, either to learn more on the stability of the casein in the milk from these species or for nutritional purposes, a section on PTMs of the caseins in the milks from other species is added at the end of the chapter.