ARS | Publication request: REVIEW OF THE CHEMISTRY OF ALPHA S-2 CASEIN AND THE GENERATION OF A HOMOLOGOUS MOLECULAR MODEL TO EXPLAIN ITS PROPERTIES

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2008
Publication Date: April 1, 2009
Citation: Farrell, H.M., Malin, E.L., Brown, E.M., Guitierrez, 2009. M. REVIEW OF THE CHEMISTRY OF ALPHA S-2 CASEIN AND THE GENERATION OF A HOMOLOGOUS MOLECULAR MODEL TO EXPLAIN ITS PROPERTIES. Journal of Dairy Science. 92:1338-1353

Interpretive Summary: Milk and dairy products represent the chief source of calcium in the typical western diet. The major proteins of milk, called caseins, carry calcium in small packages called micelles. Previous work on the comparison of goat’s and cow’s milk caseins showed that one genetic type of goat’s milk casein, regardless of breed, is much better at carrying calcium than that of other goat’s or cow’s milk. This type of goats’ milk is rich in one casein: alpha-s2-casein which comprises only up to 10% of the casein fraction in bovine milk. This particular protein has not been studied as well as the other caseins and now interest in the role of this molecule in dairy products and nutrition has been renewed. To help clarify the role of alpha-s2-casein in its structure-function relationships in milk and its possible applications in dairy products, this paper reviews the chemistry of the protein and presents a working three dimensional (3D) model for the protein. This 3D model points the way to a better understanding of the protein and its future applications in improved dairy products with enhanced nutrition and health promoting properties. In particular the model for alpha-s2-casein predicts that fractions derived from the molecule may have properties which not only aid in fighting bacteria but may also promote intestinal well being. This model completes the series of working models for the caseins produced by this group.

Technical Abstract: Alpha-s2-Casein comprises up to 10% of the casein fraction in bovine milk. The role of this protein in casein micelles has not been studied in detail in part due to a lack of structural information on the molecule. Interest in the role of this molecule in dairy products and nutrition has been renewed by work in three areas: biological activity via potentially biologically active peptides, functionality in cheeses and products and nutrition in terms of calcium uptake. To help clarify the role of alpha-s2-casein in its structure-function relationships in milk and its possible applications in dairy products, this paper reviews the chemistry of the protein and presents a working three dimensional molecular model for the protein. The three dimensional molecular model for alpha-s2-casein was produced by threading the backbone sequence of the protein onto a homologous protein: chloride intracellular channel protein-4 (CLIC-4). Overall the model is in good agreement with experimental data for the protein; however the amount of helix may be over predicted. The model does however offer a unique view of the highly positive C-terminal portion of the molecule as a surface accessible area. This region may be the site for interactions with k-carrageenan, phosphate of other anions. In addition most of the physiologically active peptides isolated from alpha-s2-casein occur in this region. This structure should be viewed as a working model with the ability to be changed as more precise experimental data is obtained.