Molecular Insights into the Conformational and Binding Behaviors of Human Serum Albumin Induced by Surface-Active Ionic Liquids

Abstract

Extensive research has been carried out to investigate the stability and function of human serum albumin (HSA) when exposed to surface-active ionic liquids (SAILs) with different head groups (imidazolium, morpholinium, and pyridinium) and alkyl chain lengths (ranging from decyl to tetradecyl). Analysis of the protein fluorescence spectra indicates noticeable changes in the secondary structure of HSA with varying concentrations of all SAILs tested. Helicity calculations based on the Fourier transform infrared (FTIR) data show that HSA becomes more organized at the micellar concentration of SAILs, leading to an increased protein activity at this level. Small-angle neutron scattering (SANS) data confirm the formation of a bead–necklace structure between the SAILs and HSA. Atomistic molecular dynamics (MD) simulation results identify several hotspots on the protein surface for interaction with SAIL, which results in the modulation of protein conformational fluctuation and stability. Furthermore, fluorescence resonance energy transfer (FRET) experiments with the intramolecular charge transfer (ICT) probe trans-ethyl p-(dimethylamino) cinnamate (EDAC) demonstrate that higher alkyl chain lengths and SAIL concentrations result in a significantly increased energy transfer efficiency. The findings of this study provide a detailed molecular-level understanding of how the protein structure and function are affected by the presence of SAILs, with potential implications for a wide range of applications involving protein–SAIL composite systems.