Food Structure


Three-dimensional (3 -D) structures derived from X-ray crystallography are important in elucidating structure- function relationships for many proteins. However, not all food proteins can be crystallized. The casei ns of bovine milk are one class of non-crysta11izable proteins (a, 1-, K-, and /3-). The complete primary and partial secondary structures of these proteins are known, but homologous proteins of known crystallographic structure cannot be found. Therefore , sequence based predictions of secondary structure were made and adjusted to conform with data from Raman and Fourier-transformed infra- red spectroscopy. With this information, 3-D structures for these caseins were built using the Sybyl molecular modeling programs. The K-casein structure contained two anti-parallel P-sheets which are predominately hydrophobic. The a,1-casein structure also contained a hydrophobic domain composed of .B-sheets as well as a hydrophilic domain ; these two are connected by a segment of ex- helix . Both the K- and a,1-caseins represent unrefined models in that they have been manipulated to remove unrealistic bonds but have not been energy-mini mized . Nevertheless the models account for the tendency of these caseins to associate. The .B-casein model appears to follow a divergent structural pattern. When subjected to energy minimization, it yielded a loosely packed structure with an ax.ial ratio of 2 to I, a hydrophobic C-terminal domain , and a hydrophilic N-terminal end. All three casein structures showed good agreement with literature concerning their global biochemical and physico-chemical properties.

Included in

Food Science Commons