Each protein folds into a unique and native structure spontaneously. However, during the unfolding or refolding process, a protein often tends to form aggregates. To establish a method to prevent undesirable protein aggregation and to increase the stability of native protein structures under deterioration conditions, two types of aggregation conditions, thermal unfolding-induced aggregation and dilution-induced aggregation from denatured state, were studied in the presence of additional amino acids and ions using lysozyme as a model protein. Among 15 amino acids tested, arginine exhibited the best results in preventing the formation of aggregates in both cases. Further biophysical studies revealed that arginine did not change the thermal denaturation temperature (T_m) of the lysozyme. The preventive effect of arginine on aggregation was not dependent on the size or isoelectric point of eight kinds of proteins tested.

Controllable membrane phase separation through the action of a synthetic photoresponsive amphiphile is reported. We studied multi-component giant vesicles formed from a ternary lipid mixture of saturated and unsaturated phospholipid and cholesterol together with the photoresponsive amphiphile. A change in the conformation of the photoresponsive amphiphile can switch membrane lateral segregation in a reversible manner. Cis-isomerization induces lateral phase separation in one-phase membranes or produces additional lateral domains in two-phase membranes. Membranes that are close to miscibility boundary show high photo-responsiveness. This is the first report on the reversible control of membrane lateral segregation triggered by a conformational change in a membrane-constituting molecule. These findings may lead to new methods for controlling membrane self-organization such as raft engineering.

Capsaicin is a natural compound that produces a warm sensation and is known for its remarkable medicinal properties. Understanding the interaction between capsaicin with lipid membranes is essential to clarify the molecular mechanisms behind its pharmacological and biological effects. In this study, we investigated the effect of capsaicin on thermoresponsiveness, fluidity, and phase separation of liposomal membranes. Liposomal membranes are a bioinspired technology that can be exploited to understand biological mechanisms. We have shown that by increasing thermo-induced membrane excess area, capsaicin promoted membrane fluctuation. The effect of capsaicin on membrane fluidity was dependent on lipid composition. Capsaicin increased fluidity of (1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membranes, while it rigidified DOPC and cholesterol-based liposomes. In addition, capsaicin tended to decrease phase separation of heterogeneous liposomes, inducing homogeneity. We imagine this lipid re-organization to be associated with the physiological warming sensation upon consumption of capsaicin. Since capsaicin has been reported to have biological properties such as antimicrobial and as antiplatelet, the results will help unravel these biological properties.