title: Binding between Saikosaponin C and Human Serum Albumin by Fluorescence Spectroscopy and Molecular Docking.
abstract: Saikosaponin C (SSC) is one of the major active constituents of dried Radix bupleuri root (Chaihu in Chinese) that has been widely used in China to treat a variety of conditions, such as liver disease, for many centuries. The binding of SSC to human serum albumin (HSA) was explored by fluorescence, circular dichroism (CD), UV-vis spectrophotometry, and molecular docking to understand both the pharmacology and the basis of the clinical use of SSC/Chaihu. SSC produced a concentration-dependent quenching effect on the intrinsic fluorescence of HSA, accompanied by a blue shift in the fluorescence spectra. The Stern-Volmer equation showed that this quenching was dominated by static quenching. The binding constant of SSC with HSA was 3.72 × 10³ and 2.99 × 10³ L·mol(-1) at 26 °C and 36 °C, respectively, with a single binding site on each SSC and HSA molecule. Site competitive experiments demonstrated that SSC bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for SSC-HSA association. The energy transfer efficiency and binding distance between SSC and HSA was calculated to be 0.23 J and 2.61 nm at 26 °C, respectively. Synchronous fluorescence and CD measurements indicated that SSC affected HSA conformation in the SSC-HSA complex. Molecular docking supported the experimental findings in conformational changes, binding sites and binding forces, and revealed binding of SSC at the interface between subdomains IIA-IIB.
authors.affiliation: Key Immunopharmacology Laboratory of Guangdong Province, Department of Pathophysiology, Institute of Inflammation and Immune Diseases, Shantou University Medical College, Guangdong 515041, China. chenyicun@yeah.net.|Department of Pharmacology, Traditional Chinese Medicine Laboratory, Shantou University Medical College, Guangdong 515041, China. chenyicun@yeah.net.
authors.forename: Yi-Cun
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Key Immunopharmacology Laboratory of Guangdong Province, Department of Pathophysiology, Institute of Inflammation and Immune Diseases, Shantou University Medical College, Guangdong 515041, China. junebulu@163.com.
authors.forename: Hong-Mei
authors.initials: HM
authors.lastname: Wang
authors.affiliation: Key Immunopharmacology Laboratory of Guangdong Province, Department of Pathophysiology, Institute of Inflammation and Immune Diseases, Shantou University Medical College, Guangdong 515041, China. nqx_1961@163.com.
authors.forename: Qing-Xia
authors.initials: QX
authors.lastname: Niu
authors.affiliation: Department of Pharmacology, Traditional Chinese Medicine Laboratory, Shantou University Medical College, Guangdong 515041, China. 15917907394@163.com.
authors.forename: Dan-Yan
authors.initials: DY
authors.lastname: Ye
authors.affiliation: Key Immunopharmacology Laboratory of Guangdong Province, Department of Pathophysiology, Institute of Inflammation and Immune Diseases, Shantou University Medical College, Guangdong 515041, China. gwliangizzy@163.com.
authors.forename: Guo-Wu
authors.initials: GW
authors.lastname: Liang
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D004735:Energy Transfer; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D012503:Saponins / Q000737:chemistry* / Q000494:pharmacology; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D012503:Saponins; D012709:Serum Albumin; D009828:Oleanolic Acid; C025759:saikosaponin D
keywords: Chaihu; Radix bupleuri; human serum albumin; molecular docking; saikosaponin C; static quenching
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