In milk, caseins (CSNs) interact with calcium phosphate (CaPO4), forming large stable colloidal particles called micelles. These micelles make it possible to maintain a supersaturated CaPO4 concentration in milk, providing the newborn with sufficient calcium phosphate for the mineralisation of calcified tissues. Human alpha-S1-casein (CSN1S1) is able to bind CaPO4 in milk. CSN1S1 forms a disulfide cross-linked heteropolymer with kappa-casein (CSN3), another CSN that is thought to stabilise micelle formation and thus preventing casein precipitation in milk (Brignon et al. 1985, Rasmussen et al. 1995, Johnson et al. 1995).