Three-Dimensional Molecular Modeling of Bovine Caseins: -Casein

¹ US Department of Agriculture, Eastern Regional Research Center, Agricultural Research Service, 600 East Mermaid Lane, Philadelphia, PA

Three-dimensional structures derived from X-ray crystallography are extremely important in elucidating relationships between structure and function for many proteins. However, not all proteins can be crystallized. The caseins of bovine milk are one class of noncrystallizable proteins. The complete primary and partial secondary structures of these proteins are known, but homologous proteins with known crystallographic structure are not available. In this report, sequence-based predictions of secondary structure were made and adjusted to conform with global secondary structures derived from Fourier transform infrared spectroscopy. With this information, a three-dimensional structure for -casein was constructed using molecular modeling computer programs. The constructed model contains two unstranded ß-sheets; both are predominately hydrophobic and capable of forming quaternary structural interaction sites with _s1-casein. This unrefined structure is in good agreement with much of the biochemical information available for -casein.

Key Words: casein structure • protein functionality • milk proteins

Submitted on December 3, 1990
Accepted on February 25, 1991