Dependence of the interfacial behavior of beta-casein on phosphoserine residues.

The role of the phosphoserine residues on the dynamical and structural properties of beta-casein was studied by molecular dynamics of the protein in water/lipid interfacial regions. The initial protein structure adopted in the modeling was that proposed for bovine beta-casein A2, where the five phosphoserine residues, originally present in its primary structure, were partially or totally substituted by serine residues. The simulations revealed a dependence of the interfacial behavior of beta-casein on the phosphorylation grade. When only partially dephosphorylated, the protein showed a similar behavior as that observed for the original beta-casein reported in previous work. During dynamics, the protein migrated from the aqueous environment towards the lipid medium, and remained attached to the interface separating both media. Quite different was the dynamics of the totally dephosphorylated beta-casein, that did not perceive the interface and immersed incessantly into lipid medium. The results suggest that the phosphoserine residues appear to be, in fact, intrinsically related to the mechanisms of beta-casein emulsion stabilization.

Folding interpenetration in a gliadin model: the role of the characteristic octapeptide motif.

A model of a rheologically relevant protein, omega-gliadin, is proposed and studied in this work by means of molecular dynamics techniques. The model is based on an octapeptide repeat motif that is experimentally described as characteristic of that protein and as constituting it almost entirely. The initial molecular structure consisted of 20 such repeats. It was optimized and the dynamics developed along 980 ps, at dielectric constant epsilon = 80. Remarkable structural features were observed for the model built, such as an elongated twisted tubular overall structure with a peculiar interpenetrating folding pattern, of a very regular character, organized strand formation, topologically segregated sites on the outer surface with an alternate hydrophilic/hydrophobic character and a hydrophilic inner cavity. Dynamics produced significantly more relaxed structures, but was not able to change the main geometric features presented by the original structure. Preliminary attempts of correlating some structural/dynamic aspects observed for the model with features of gliadin rheological behavior are presented.