title: Novel stereoselective bufadienolides reveal new insights into the requirements for Na(+), K(+)-ATPase inhibition by cardiotonic steroids.
abstract: Cardiotonic steroids (CTS) are clinically important drugs for the treatment of heart failure owing to their potent inhibition of cardiac Na(+), K(+)-ATPase (NKA). Bufadienolides constitute one of the two major classes of CTS, but little is known about how they interact with NKA. We report a remarkable stereoselectivity of NKA inhibition by native 3β-hydroxy bufalin over the 3α-isomer, yet replacing the 3β-hydroxy group with larger polar groups in the same configuration enhances inhibitory potency. Binding of the two (13)C-labelled glycosyl diastereomers to NKA were studied by solid-state NMR (SSNMR), which revealed interactions of the glucose group of the 3β- derivative with the inhibitory site, but much weaker interactions of the 3α- derivative with the enzyme. Molecular docking simulations suggest that the polar 3β-groups are closer to the hydrophilic amino acid residues in the entrance of the ligand-binding pocket than those with α-configuration. These first insights into the stereoselective inhibition of NKA by bufadienolides highlight the important role of the hydrophilic moieties at C3 for binding, and may explain why only 3β-hydroxylated bufadienolides are present as a toxic chemical defence in toad venom.
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Hong-Jin
authors.initials: HJ
authors.lastname: Tang
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Ruan
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Tian
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Guang-Ping
authors.initials: GP
authors.lastname: Liang
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Wen-Cai
authors.initials: WC
authors.lastname: Ye
authors.affiliation: Department of Chemistry, University of Lancaster, Lancaster LA1 4YB, UK.
authors.forename: Eleri
authors.initials: E
authors.lastname: Hughes
authors.affiliation: Department of Biomedicine, Aarhus University DK-8000, Aarhus, Denmark.
authors.forename: Mikael
authors.initials: M
authors.lastname: Esmann
authors.affiliation: Department of Biomedicine, Aarhus University DK-8000, Aarhus, Denmark.
authors.forename: Natalya U
authors.initials: NU
authors.lastname: Fedosova
authors.affiliation: Graduate Institute of Biotechnology, National Chung-Hsing University Taichung 40227, Taiwan, China.
authors.forename: Tse-Yu
authors.initials: TY
authors.lastname: Chung
authors.affiliation: Graduate Institute of Biotechnology, National Chung-Hsing University Taichung 40227, Taiwan, China.
authors.forename: Jason T C
authors.initials: JT
authors.lastname: Tzen
authors.affiliation: College of Pharmacy, Jinan University, Guangzhou city, Guangdong province 510632, P. R. China.
authors.forename: Ren-Wang
authors.initials: RW
authors.lastname: Jiang
authors.affiliation: Department of Chemistry, University of Lancaster, Lancaster LA1 4YB, UK.
authors.forename: David A
authors.initials: DA
authors.lastname: Middleton
mesh_terms: D000818:Animals; D002018:Bufanolides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D002025:Bufonidae; D002247:Carbon Isotopes; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D002301:Cardiac Glycosides / Q000737:chemistry / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D062105:Molecular Docking Simulation; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D002018:Bufanolides; D002247:Carbon Isotopes; D002301:Cardiac Glycosides; D000254:Sodium-Potassium-Exchanging ATPase; C022777:bufalin