s2kasein

S2-casein, also referred to as alpha-s2-casein (αs2-casein), is a phosphoprotein that is part of milk milk’s casein fraction. It is one of the four major caseins found in many mammalian milks, alongside alpha-s1-casein, beta-casein, and kappa-casein. In cattle and other ruminants, αs2-casein is typically encoded by the CSN1S2 gene and produced by mammary-gland tissue.

The protein is characterized by phosphorylation at multiple serine residues, which enables binding of calcium and interaction with other casein molecules to form casein micelles. These micelles contribute to milk stability, influence calcium transport, and affect the texture and processing properties of dairy products. αs2-casein participates in gelation and cheese yield through its role in micelle structure and calcium sensitivity.

Genetic variation in the CSN1S2 gene can give rise to different αs2-casein variants, and the relative abundance of αs2-casein can vary by species and dairy breed. Such variation can influence milk composition and properties relevant to processing, including coagulation behavior and cheese quality. In addition to its industrial relevance, caseins, including αs2-casein, are dietary proteins that can be allergenic for some individuals, though patterns of allergenicity are complex and not limited to a single casein type.

See also casein, alpha-s1-casein, beta-casein, kappa-casein, and CSN1S2.