Investigations of the interactions of peimine and peiminine with human serum albumin by spectroscopic methods and docking studies

The primary objective of this study is to evaluate the interactions of human serum albumin (HSA) with peimine (PE) and peiminine (PEN) in physiological conditions by fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy, Raman spectroscopy, and molecular modeling. PE and PEN were isolated from Bulbus Fritillariae thunbergii miq. The binding constants Ka and the number of binding sites n were calculated at different temperatures. Enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) were also determined. The results suggested that quenching of HSA fluorescence by PE and PEN is a static process. Three-dimensional fluorescence, FT-IR, CD, and Raman spectra showed that the binding of PE and PEN to HSA can induce conformational changes in the latter. Moreover, important differences in binding ability were observed between PE and PEN, and PE showed stronger binding affinity to HSA than PEN. -- Highlights: • This paper provides the whole separation and purification process of peimine and peiminine and their detailed structure information. • A comparative study between peimine and peiminine shows the difference of their structure affects their binding ability to HSA. • FT-IR, three-dimensional fluorescence, CD and Raman spectra were used to explain the conformational changes of HSA reasonably. • Time-resolved fluorescence was used to distinguish the quenching mechanisms