Elucidation of the interaction between apo-transferrin and indisulam via multi-spectroscopic techniques and molecular modeling

Apo-transferrin (apo-TRF) is a vital protein for maintaining iron balance in the body, which is produced by the liver. Indisulam (IDM) has been extensively used to treat cancer in clinical study and has been identified as a molecular glue. Iron imbalances in the body are believed to encourage the growth and spread of cancer cells. Thus, understanding the interactions between apo-TRF and IDM may serve as a foundation for identifying novel therapeutic strategies for cancer associated with iron imbalances. In this study, multi-spectroscopic methods and computer simulations were employed to explore the binding mode between apo-TRF and IDM, as well as to investigate IDM's impact on the biological functions of apo-TRF. Multi-spectroscopic studies indicated that IDM and apo-TRF formed binary complexes with K_a of 1.274 × 10⁴ M^-1 at 298 K. The H-bonds and van der Waals forces were the dominant interaction forces based on an analysis of the thermodynamic parameters (ΔH^θ = -37.565 kJ/mol, ΔS^θ = -46.665 J mol^-1 K^-1). Three-dimensional (3D) and circular dichroism (CD) spectra revealed the conformational of apo-TRF changed by IDM, resulting in a looser and more unfolded structure. With escalating concentrations of IDM, a notable reduction in the binding affinity between apo-TRF and Fe³⁺ was observed, indicating that IDM could potentially alter iron transfer mediated by apo-TRF. Molecular docking analysis indicated that IDM docked in the apo-TRF iron-binding pocket. After in-depth analysis of the molecular dynamic results, it was found that Asp392 played an important role in this interaction. In addition, accessible surface area (ASA) values of key residues (Tyrosine, Aspartate, and Histidine) for iron transfer were altered, which could be a possible reason for the change in iron transport.