β-cyclodextrin saves lysozyme from the clutches of 1-alkylsulfonates

Non-covalent interactions between proteins and small molecules are one of the factors, along with pH and temperature, that have a significant impact on protein function, stability and biological activity. Reversible protein folding induced by molecular crowding can be controlled by introducing ligands that compete with the protein for small molecules. One example is lysozyme (Lys), which unfolds in the presence of ligands that contain hydrophobic groups in their structure, such as 1-alkylsulfonates (KXS). In this paper, a series of experimental methods, namely circular dichroism spectroscopy, isothermal titration calorimetry, conductometric titration and differential scanning calorimetry, supported by in silico analysis, have been applied to characterise the process of reversibility changes of lysozyme structure in the presence of 1-alkylsulfonates with different hydrophobic chain lengths and β-cyclodextrin (β-CD) used as a strong competitive KXS-binding ligand. It has been shown that the observed structural changes can be reversed by introducing β-CD into the system, which, due to its higher affinity for KXS in comparison to lysozyme, effectively binds small ligands and so allows the protein to refold.