Investigation on the interaction of antibacterial drug moxifloxacin hydrochloride with human serum albumin using multi-spectroscopic approaches, molecular docking and dynamical simulation

The interaction between moxifloxacin hydrochloride (MOXH) and human serum albumin (HSA) was experimentally and simulatively investigated. Fluorescence quenching presented that MOXH bound to HSA via a static process, resulting in the formation of MOXH–HSA complex. This quenching mechanism was further verified by time-resolved fluorescence. Binding constants (Ka) of the complex were found to be 105 L mol−1 according to fluorescence data, and the calculated thermodynamic parameters indicated that hydrogen bonds and van der Waals force played key roles in the binding process. The UV-vis absorption, synchronous fluorescence, three-dimensional fluorescence, and circular dichroism spectra suggested that binding with MOXH induced the conformational changes on HSA; the hydrophobicity around tryptophan residues increased, the α-helix content increased, whereas the β-sheet and turn content of HSA decreased. Displacement experiments demonstrated that MOXH mainly bound to site I of HSA. Molecular docking results supported the active site and showed that the diazabicyclo of MOXH inserted into the hydrophobic pocket of HSA. Molecular dynamics simulation further ascertained that MOXH steadily bound to site I of HSA. In conclusion, hydrogen bonds and VDW force played major roles in stabilizing the MOXH–HSA complex, and hydrophobic force was also involved in the binding process.