Spectroscopy and molecular docking approach for investigation on the binding of nocodazole to human serum albumin.

The interaction between nocodazole (Nz) and human serum albumin (HSA) under controlled physiological condition (pH 7.4) is examined using absorption, emission, fluorescence lifetime (FLT) and circular dichroism (CD) spectroscopic techniques. The binding constant (order of 10 M) from UV-vis and fluorescence spectroscopy reveals a strong interaction between Nz and HSA. Fluorescence quenching study shows that Nz binds with HSA through static quenching process. It is induced by formation of Nz-HSA complex because the Stern-Volmer quenching constant is inversely correlated with the temperature which is further verified by time-resolved fluorescence spectroscopy. The thermodynamic parameters at different temperatures indicate that the binding process is spontaneous where hydrogen bonding interactions and Van der Waals forces play major roles during the interaction between Nz and HSA. By means of spectroscopy and molecular modeling, we have discovered and interpreted the alteration of the secondary structure of HSA by Nz complexation. Synchronous, three-dimensional fluorescence and CD spectroscopic results reveal that the addition of Nz to HSA affects changes in the micro-environment and conformation of HSA. According to Förster Resonance Energy Transfer (FRET), the binding distance (r) between Nz and residue of HSA is <8 nm with excellent energy efficiency. The docking study suggests that nocodazole binds at Domain IIA in the hydrophobic pocket of human serum albumin.