Interactions and self-assembly of globular proteins: Mechanism and properties of formed supramolecular structures
Résumé
Sustainability in food manufacture involves a profound reasoning of the way food are produced. Reducing energy input during food processing and optimizing ingredient formulation in order to meet both sensorial acceptance and nutritional benefit through a controlled release of macro- and micronutriments constitute great challenges for food industries. Controlled self-assembly of molecules into biomaterials throughout bottom-up approach is a promising way to achieve these goals. Because of their omnipresence in food systems, proteins are the focus of many attempts for their use as building blocks for such biomaterials. For instance, the apo form of α-lactalbumin (α-LA) and β-lactoglobulin are able to self-assemble into well-defined microspheres in the presence of an oppositely charged protein such as lysozyme (LYS).1 Formation and destabilization of microspheres are inducible by changing the physicochemical conditions. Because of this reversibility, such microspheres could be used to trap, protect during processing and storage, carry and deliver bioactives. However, to complete this challenge, a perfect understanding of protein assembly and disassembly mechanisms are necessary. In this communication we address the mechanism of formation of microspheres of α-LA and LYS from the molecular scale to the micropheres. One of the first events in the mechanism of formation of microspheres is a specific interaction between a α-LA and LYS leading to a heterodimer.2 Probably throughout charge screening, α-LA/LYS heterodimers rapidly self-assembled into nanometer sized-aggregates. These small entities further aggregate into clusters following a diffusion limited mechanism (DLCA) and fuse upon physical contact into spherical microspheres. The driving force for the reorganisation of the clusters into microspheres is suggested to be the decrease of the total surface free energy. However, the reorganization of the clusters was only inducible when the temperature was increased above 30°C, temperature above which a α-LA adopt a molten globule structure. We put forward that the higher flexibility of α-LA above 30°C may facilitate clusters – microspheres transition.