Exploring the HSA/DNA binding behavior of p-Synephrine, a naturally occurring phenyl ethanol amine with anti-adipogenic activity: multi spectroscopic and molecular dynamics approaches
Exploring the HSA/DNA binding behavior of p-Synephrine, a naturally occurring phenyl ethanol amine with anti-adipogenic activity: multi spectroscopic and molecular dynamics approaches
Introduction: In traditional Chinese medicine, the Citrus aurantium plant is widely exerted for various problems such as indigestion, diarrhea, and respiratory problems. It contains multiple active ingredients such as p-Synephrine (SN), a phenyl-ethanolamine that is believed to exert lipolytic and thermogenic activity through the induction of beige adipocyte differentiation (1). SN has some structural similarities to ephedrine which was prohibited by the FDA in 2004 due to its association with cases of seizure and heart attack. However, according to many peer-reviewed studies, despite the similarities to ephedrine, SN consumption in typical doses results in no cardiovascular effects (2, 3). Nonetheless, this study aimed to provide a comprehensive and complete profile of the biomolecular interactions of SN to human serum albumin (HSA) and calf thymus DNA (ct-DNA) using a detail-oriented approach through a combination of different biophysical methods and molecular docking.
Methods: A wealth of information has been produced through a combination of the following protocols: fluorescence spectroscopy, Resonance Light Scattering (RLS), and viscometry measurements. The molecular docking method was employed to investigate the exact binding site of ligands in interaction with HSA and ctDNA.
Results: The emission spectra of HSA in the presence and absence of SN are demonstrated in Fig. 1. Obviously, in the presence of SN, the fluorescence intensity of HSA has been dramatically reduced and slightly blue-shifted towards lower wavelengths. Fig. 2 illustrates the RLS spectra of the HSA-SN complex. At first glance, it is observable that upon the addition of SN to the HSA solution, the RLS intensity increased. Meanwhile, the gradual addition of ct-DNA to SN solution induced an obvious quenching in the SN-DNA spectra. Moreover, the addition of various concentrations of SN to the ct-DNA solution resulted in a negligible change in the relative viscosity. Docking results indicate the positioning of SN in the Sudlow site I which is located in subdomain IIA of HSA. While the docking outcomes of the ct-DNA-SN complex show the propensity of SN towards the grooves of the ct-DNA.
Conclusion: The ability of SN to reversibly interact with HSA has been manifested through the occurrence of quenching in the emission spectra (Fig. 1). This interaction occurs spontaneously and consequently changes the conformation of the protein (4). In accordance with RLS data (Fig. 2), the interaction between SN and HSA has led to the formation of a new complex that is larger in size and shape. As confirmed by molecular docking, SN is able to attach to Arg 257, Arg 218, and His 242. This strong interaction with HSA is facilitated through hydrogen bonds and ionic interactions.
As revealed by fluorescence data, SN is clearly amenable to forming a complex with ct-DNA and changing its conformation. The relative viscosity of ct-DNA remained almost unaffected as various concentrations of SN is added to the solution which further suggests the tendency of SN to interact with the grooves of ct-DNA (5). The docking results of the DNA-SN complex confirm the previous findings. This method has also revealed the ability of SN to bind to ct-DNA through hydrogen bonds and H-pi interaction.