Influence of Calcium Ions on the Membrane Binding of S100B Protein

The S100B protein plays diverse roles in cellular mechanisms, particularly at the membrane, where it is suggested to exhibit chaperone-like functions, stabilizing the conformation of the p53 protein and facilitating its nuclear translocation and accumulation. However, the membrane binding ability of the S100B protein and the parameters affecting these interactions remain unclear. This study thus explores the membrane binding of S100B using the Langmuir monolayer model coupled with surface tensiometry in order to better understand its role where lipids are involved in its environment. S100B was overexpressed in <i>E. coli</i> and purified by affinity chromatography. The binding parameters and kinetics of purified S100B were measured using surface tensiometry in the presence and absence of calcium ions. S100B preferentially interacts with unsaturated phospholipids, particularly those with PE and PS head groups. Also, the presence of calcium ions enhances these interactions by inducing conformational changes in the S100B structure. The binding kinetics revealed increased interaction with unsaturated lipids, underscoring the importance of the lipid environment in modulating the S100B function. In addition, the interaction observed in the monomeric form indicates that dimerization is critical for S100B's effective membrane binding. These findings provide new insights into S100B's interaction with phospholipids, enhancing our understanding of the factors influencing its membrane behavior.