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Sandbox WWCAlpha-S1-Casein

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Casein consists of a group of proteins found in all mammal milks, including αs1-, αs2-, and β-casein (calcium-sensitive caseins), κ-casein (calcium insensitive).[1] Although αs1-CN is the predominant casein in bovine milk, the ratios of caseins vary considerably by species, and in human milk β-casein is predominant.[2][3]

Calcium-sensitive (CS) caseins such as αs1-CN bind calcium phosphate (CaP), and high concentrations of CaP will cause these caseins to precipitate. In milk, huge complexes are formed from CaP, calcium-sensitive caseins, and calcium-insensitive (CI) caseins. Precipitation of the CS caseins in these complexes is prevented by CI caseins stabilizing the complex to form a micelle. In addition to providing nutritive protein to mammalian neonates, these micelles supply calcium and inorganic phosphate at levels much higher than would be expected if the molecules were simply dissolved in the milk.[4] Unlike whey proteins, which include all non-casein proteins, casein micelles are relatively heat stable, although denaturation of the whey protein β-lactoglobulin at high temperatures can result in interactions with micellar κ-casein that alters the structure of the micelle surface.[5]

Preceding the formation of casein micelles, binding of CS casein to the nuclei CaP forms CaP nanoclusters. It has been suggested that the rheomorphic (non-rigid) structure of CS caseins is what allows such rapid CaP binding [6]

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References

  1. ↑ J. Dairy Sci., 67, 1599-1631, 1984, and from Table 1, J. Dairy Sci., 68, 2195-2205, 1985
  2. ↑ Kawasaki K, Lafont AG, Sire JY. The evolution of milk casein genes from tooth genes before the origin of mammals. Mol Biol Evol. 2011 Jul;28(7):2053-61. doi: 10.1093/molbev/msr020. Epub 2011 Jan , 18. PMID:21245413 doi:http://dx.doi.org/10.1093/molbev/msr020
  3. ↑ McSweeney, P. (2009). Nutritional Aspects of Milk Proteins. In Advanced dairy chemistry (3rd ed., Vol. 1). New York: Springer-Verlag.
  4. ↑ McSweeney, P. (2009). Nutritional Aspects of Milk Proteins. In Advanced dairy chemistry (3rd ed., Vol. 1). New York: Springer-Verlag.
  5. ↑ Fennema, O. (1996). Characteristics of Milk. In Food chemistry (3rd ed., p. 865). New York: Marcel Dekker.
  6. ↑ Uversky VN, Dunker AK. Understanding protein non-folding. Biochim Biophys Acta. 2010 Jun;1804(6):1231-64. doi:, 10.1016/j.bbapap.2010.01.017. Epub 2010 Feb 1. PMID:20117254 doi:http://dx.doi.org/10.1016/j.bbapap.2010.01.017
  7. ↑ Masoodi, T. A., & Shafi, G. (2010). Analysis of casein alpha S1 & S2 proteins from different mammalian species. Bioinformation, 4(9), 430–435.
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