Interplay of interactions between micelles and fibrils of casein proteins

Abstract

ABSTRACT Kappa-casein (κCΝ) and beta-casein (βCN) are two of the four milk proteins that constitute the milk micelles (casein micelles), ∼ 250 nm aggregates held by calcium-phosphate bridges, designed by nature to deliver nutrients to the neonate. κCN is localized at the surface of the micelle, while βCN, together with other caseins, is located inside the micelle. At pathological conditions κCN undergoes fibrilization. In an earlier study we showed that fibrils formation and growth can be hindered in mixed κCN/βCN solutions by the formation of classical core-shell mixed micelles. The present study focuses on a later stage, where κCN fibrils are already formed. Using ITC, we find strong adsorption of βCN onto the fibrils, probably in the form of micelles as indicated by Cryo-TEM and SAXS. The results of the interaction between κCN fibrils and another amphiphile, Lutrol (Pluronic F-127), also demonstrated the adsorption. Some differences were found in the manner of adsorption of the amphiphiles. βCN adsorption is manifested at relatively high concentrations, after its demicellization/micellization. Lutrol, on the other hand, adsorbs already upon initial ITC injections, in parallel with demicellization, as indicated by splitting of the peaks. By deconvolution of the splitting peaks, the contributions of demicellization and adsorption of Lutrol were resolved. We conclude that the polymer adsorption is an additional factor suppressing κCN fibrillization and fibril growth. The decorated κCN fibrils may be considered as a new functional material.