Interplay of interactions between micelles and fibrils of casein proteins

Kappa-casein (irCN) and beta-casein (beta CN) 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. irCN is localized at the surface of the micelle, while beta CN, together with other caseins, is located inside the micelle. At pathological conditions irCN undergoes fibrilization. In an earlier study we showed that fibrils formation and growth can be hindered in mixed irCN/beta CN solutions by the formation of classical coreshell mixed micelles. The present study focuses on a later stage, where irCN fibrils are already formed. Using ITC, we find strong adsorption of beta CN onto the fibrils, probably in the form of micelles as indicated by Cryo-TEM and SAXS. The results of the interaction between irCN fibrils and another amphiphile, Lutrol (Pluronic F-127), also demonstrated the adsorption. Some differences were found in the manner of adsorption of the amphiphiles. beta CN 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 irCN fibrillization and fibril growth. The decorated irCN fibrils may be considered as a new functional material.

Automated summary

The study found that beta-CN strongly adsorbs onto formed irCN fibrils, likely in the form of micelles, while another amphiphile, Lutrol, also demonstrated adsorption onto the fibrils. Differences were found in the adsorption of the two, with beta-CN adsorbing at higher concentrations after its demicellization/micellization, and Lutrol adsorbing early on during initial injections, indicating suppression of irCN fibrilization and growth by polymer adsorption.