Interactions between stipuol enantiomers and human serum albumin

Natural polyacetylenes occur in food and herbal plants, have a wide range of bioactivities, and are recognized as important nutraceuticals. Stipuol is a natural polyacetylene present in the edible plant Panax notoginseng. The present study was aimed to study interactions of rac-stipuol and its enantiomers with human serum albumin (HSA) using multi-spectroscopic, molecular modeling and microscale thermophoresis. Steady-state and time-resolved fluorescence spectra manifest that the fluorescence quenching mechanism is mainly static in type. The bindings of (S)-stipuol, (R)-stipuol, rac-stipuol lead to some microenvironmental and slight conformational changes of HSA. Competitive ligand displacement experiments and molecular modeling studies revealed that stipuol enantiomers bind to HSA at subdomain III (site IIA). The calculated values of Ka and Kd showed that (R)-stipuol had a stronger binding affinity than (S)-stipuol. The results are informative for use of stipuol as a nutraceutical to improve human health.