Study of bovine β-casein at water/lipid interface by molecular modeling

Structural properties of p-casein were studied by techniques that permit modeling of the dynamics of proteins in solvents and in water/lipid interfacial regions. In this work, aqueous and lipid media were treated as continua, characterized by their dielectric constants, and a discontinuity plane surface, separating both media, resulted in a frictionless interface model. A proposed distended three-dimensional structure for beta -casein was adopted which, after optimization and termalization, evolved to a more folded one in the water milieu. This: compacted structure was able to keep the spatial separation between charged phosphoserine residues and hydrophobic amino acids. The simulation results with an interface reproduced the experimentally observed amphiphilic behavior of beta -casein. The protein, that at the beginning of the simulation was at rest in the aqueous medium, displaced itself towards the lipid medium, remaining at the separation interface after as long as 1 ns. The conformational analysis of beta -casein during the dynamics indicated that the protein evolved to more stable and structured conformations in me aqueous medium, further increasing this structure and stability when inside the lipid phase at the interface. The structure observed was able to explain several experimental data of beta -casein adsorbed at lipid interfaces. (C) 2001 Elsevier Science B.V. All rights reserved.