An energy-minimized casein submicelle working model.
To develop a molecular basis for structure-function relationships of the complex milk protein system, an energy-minimized, three-dimensional model of a casein submicelle was constructed consisting of kappa-casein, four alpha s1-casein, and four beta-casein molecules. The models for the individual caseins were from previously reported energy-minimized, three-dimensional structures. Docking of one kappa-casein and four alpha s1-casein molecules produced a framework structure through the interaction of two hydrophobic antiparallel sheets of kappa-casein with two small hydrophobic antiparallel sheets (residue 163-174) of two preformed alpha s1-casein dimers. The resulting structure is approximately spherically symmetric, with a loose packing density; its external portion is composed of the hydrophilic domains of the four alpha s1-caseins, while the central portion contains two hydrophbic cavities on either side of the kappa-casein central structure. Symmetric and asymmetric preformed dimers of beta-casein formed from the interactions of C-terminal beta-spiral regions as a hinge point could easily be docked into each of the two central cavities of the alpha-kappa framework. This yielded two plausible energy-minimized, three-dimensional structures for submicellar casein, one with two symmetric beta-casein dimers and one with two asymmetric dimers. These refined submicellar structures are in good agreement with biochemical, chemical, and solution structural information available for submicellar casein.
Kumosinski
T F
TF
Eastern Regional Research Center, ARS, USDA, Philadelphia, Pennsylvania 19118, USA.
King
G
G
Farrell
H M
HM
D000818:Animals; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary
D002364:Caseins