Work

Probing the binding mechanism of chemotherapeutic drug, procarbazine with BSA using multi-spectroscopic, calorimetric and computational techniques

Year: 2026

Type: article

Abstract: Understanding drug–protein interactions in buffer media is essential for unravel the pharmacokinetics and therapeutic efficacy of drug. In this project, we explore the interactions involved in binding mechanism of the chemotherapeutic drug procarbazine (PCZ) with BSA (Bovine Serum Albumin) using a multi-spectroscopic and computational approaches. UV–Visible absorption together with steady-state, synchronous, and 3D-excitation emission matrix fluorescence spectroscopy reveal static quenching of BSA fluorescence upon PCZ addition, suggesting complex formation with a binding constant of 1.36 × 10 5 M −1 obtained from UV–Visible spectroscopy accompanied by microenvironmental alterations around aromatic residues. Fluorescence quenching analysis yielded a Stern–Volmer quenching constant corresponding to a bimolecular quenching constant (K q of 11.23 × 10 13 Lmol −1 s −1 and a Gibbs free energy change (ΔG°) of −29.21 kJ mol −1 . Isothermal titration calorimetry revealed a cumulative binding constant of 4.57 × 10 −5 M −1 , with primary and secondary binding constants of 4.02 × 10 −3 M −1 and 1.20 × 10 2 M −1 , respectively. Raman Spectroscopy, Circular Dichroism and FTIR spectroscopy further indicated a significant reduction of α-helical content from 66.51% to 56.88%, reflecting partial unfolding and secondary structural rearrangements. Molecular docking identified PCZ binding near Sudlow site I, stabilized through formation of H-bond with Asp323 and hydrophobic interactions with surrounding amino acid residues. The Gibbs binding free energies obtained from fluorescence spectroscopy (−29.21 kJ mol −1 , ITC (−31.36 kJ mol −1 ), and molecular docking (−28.45 kJ mol −1 ) were in close agreement, supporting the consistency of the experimental and computational findings. Further, the conformational stability of drug-protein complex was confirmed by Molecular dynamics simulations of 100 ns period, while SASA analysis showed increased solvent exposure (171.03 Å) of hydrophobic residues upon binding. Complementary DFT calculations performed on the free and docking-derived ligand conformations revealed small variations in HOMO–LUMO energy gap (5.116 → 5.037 eV) and global reactivity descriptors, indicating modest conformationally induced changes in the electronic properties of procarbazine. These findings provide comprehensive insights into the conformational dynamics and binding energetics of BSA-PCZ interactions, advancing our molecular-level understanding of drug transport and stability in biological fluids.

Source: Journal of Molecular Liquids

DOI: 10.1016/j.molliq.2026.129838