Molecular recognition of a Novel thiazolidinedione–morpholine-based ionic liquid salt by HSA: spectroscopic and molecular dynamics analysis
TL;DR
The combined spectroscopic and computational findings indicate a spontaneous association of moderate affinity between TMH-IL salt and HSA, with molecular docking predicting preferential recognition of Sudlow's site I, while the overall structural integrity of HSA is largely preserved upon ligand binding.
Abstract
Human serum albumin (HSA) is the most abundant transport protein in human plasma and plays a crucial role in the pharmacokinetic behavior of therapeutic agents. In the present study, the interaction between a newly synthesized thiazolidinedione-morpholine-based ionic liquid salt (TMH-IL) and HSA was systematically investigated using spectroscopic techniques in combination with molecular docking and molecular dynamics (MD) simulations. Steady-state fluorescence spectroscopy revealed concentration-dependent quenching of the intrinsic fluorescence of HSA. Temperature-dependent Stern–Volmer analysis supported a predominantly static quenching mechanism, as evidenced by decreases in both the Stern–Volmer constant (KSV) and binding constant (Ka) with increasing temperature. The binding constants were on the order of 104–105 M−1, indicating moderate affinity between TMH-IL salt and HSA. Thermodynamic analysis yielded negative values of ΔH (−73.08 kJ mol−1), ΔS (−155 J mol−1 K−1), and ΔG, indicating a spontaneous and enthalpy-driven binding process. UV-vis absorption spectroscopy showed concentration-dependent absorption changes, providing complementary evidence for HSA-TMH-IL interaction. FT-IR deconvolution of the amide I region revealed only minor changes in HSA secondary structure, with the α-helical content decreasing from 62.03% to 60.16% upon ligand binding. Consistently, circular dichroism (CD) spectroscopy showed minor reductions in ellipticity at 208 and 222 nm while preserving the characteristic α-helical spectral profile. Three-dimensional fluorescence spectroscopy further indicated perturbation of the Trp214 microenvironment without substantial conformational disruption. Molecular docking predicted Sudlow's site I (subdomain IIA) as the most favorable binding region among the investigated HSA sites. The co-docked anion–cation system yielded the highest ChemPLP score, and interaction analysis revealed hydrophobic contacts and hydrogen-bonding interactions with key residues within the binding cavity. Comparative 150 ns MD simulations of free HSA and the HSA-TMH-IL complex showed that ligand binding did not substantially destabilize the protein or alter its overall compactness. RMSD, RMSF, Rg, SASA, secondary-structure, and hydrogen-bond analyses collectively indicated preservation of the overall HSA architecture, accompanied by limited local conformational rearrangements and persistent protein–ligand interactions. Overall, the combined spectroscopic and computational findings indicate a spontaneous association of moderate affinity between TMH-IL salt and HSA, with molecular docking predicting preferential recognition of Sudlow's site I, while the overall structural integrity of HSA is largely preserved upon ligand binding.