Review of the chemistry of alphaS2-casein and the generation of a homologous molecular model to explain its properties.
alpha(S2)-Casein (alpha(S2)-CN) comprises up to 10% of the casein fraction in bovine milk. The role of alpha(S2)-CN in casein micelles has not been studied in detail in part because of a lack of structural information on the molecule. Interest in the utilization of this molecule in dairy products and nutrition has been renewed by work in 3 areas: biological activity via potentially biologically active peptides, functionality in cheeses and products, and nutrition in terms of calcium uptake. To help clarify the behavior of alpha(S2)-CN 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 3-dimensional molecular model for this casein. The model was produced by threading the backbone sequence of the protein onto a homologous protein: chloride intracellular channel protein-4. Overall, the model is in good agreement with experimental data for the protein, although the amount of helix may be over-predicted. The model, however, offers 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 kappa-carrageenan, phosphate, and other anions. In addition, most of the physiologically active peptides isolated from alpha(S2)-CN occur in this region. This structure should be viewed as a working model that can be changed as more precise experimental data are obtained.
Farrell
H M
HM
Dairy Processing and Products Research Unit, USDA, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. harsuefar@aol.com
Malin
E L
EL
Brown
E M
EM
Mora-Gutierrez
A
A
D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry*; D018118:Chloride Channels / Q000737:chemistry; D006801:Humans; D021621:Imaging, Three-Dimensional; D008958:Models, Molecular; D017434:Protein Structure, Tertiary
D002364:Caseins; D018118:Chloride Channels