Studies of the interaction between demeclocycline and human serum albumin by multi-spectroscopic and molecular docking methods.

This study was designed to examine the interaction of demeclocycline (DMCTC) with human serum albumin (HSA) by multi-spectroscopic and molecular docking methods. The inner filter effect was corrected before we calculated the binding parameters. Fluorescence and UV-vis spectroscopy revealed that DMCTC induced the fluorescence quenching of HSA though a static quenching procedure. Thermodynamic analysis by Van Hoff equation found enthalpy change (ΔH) and entropy change (ΔS) were -53.01 kJ mol(-1) and -65.13 J mol(-1)K(-1), respectively, which indicated hydrogen bond and van der Waals force were the predominant force in the binding process. According to fluorescence resonance energy transfer (FRET), the specific binding distances between Trp-214 (donor) and DMCTC (acceptor) were 3.18 nm. Through site marker competitive experiments, subdomain IIA of HSA has been assigned to possess the high-affinity binding site of DMCTC. The three dimensional fluorescence showed that the conformation of HSA was changed after its complexation with DMCTC, and the alternations of protein secondary structure were quantitatively calculated from FT-IR with reduction of α-helices content about 4.8%, β-sheet from 30.3% to 21.6% and with increases of β-turn from 15.6% to 22.2%. Furthermore, the binding details between DMCTC and HSA were further confirmed by molecular docking studies, which revealed that DMCTC was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, polar forces and π-π interactions. Moreover, the coexist metal ions such as Al(3+), Fe(3+), Cu(2+), Cr(3+) and Cd(2+) can decrease the binding constants of DMCTC-HSA.