Binding of helicid to human serum albumin: a hybrid spectroscopic approach and conformational study.

The interaction between human serum albumin and helicid was studied by steady-state fluorescence, ultraviolet-visible, circular dichroism, Fourier transform infrared techniques and molecular modeling. The binding site numbers, association constants, and corresponding thermodynamic parameters were used to investigate the quenching mechanism. The alternations of protein secondary structure in the presence of helicid were demonstrated using synchronous fluorescence, Fourier transform infrared, circular dichroism and three-dimensional fluorescence spectra. The molecular modeling results revealed that helicid could bind to hydrophobic pocket of HSA with hydrophobic and hydrogen bond force. The binding site of helicid in HSA was ascertained. Moreover, an apparent distance of 3.33 nm between the Trp214 and helicid was obtained via fluorescence resonance energy transfer method.