Members of the Viola genus play important roles in traditional Asian herbal medicine. This study investigates the ability of Viola odorata L. extracts to inhibit Na+,K+-ATPase, an essential animal enzyme responsible for membrane potential maintenance. The root extract of V. odorata strongly inhibited Na+,K+-ATPase, while leaf and seeds extracts were basically inactive. A UHPLC-QTOF-MS/MS metabolomic approach was used to identify the chemical principle of the root extract's activity, resulting in the detection of 35,292 features. Candidate active compounds were selected by correlating feature area with inhibitory activity in 14 isolated fractions. This yielded a set of 15 candidate compounds, of which 14 were preliminarily identified as procyanidins. Commercially available procyanidins (B1, B2, B3 and C1) were therefore purchased and their ability to inhibit Na+,K+-ATPase was investigated. Dimeric procyanidins B1, B2 and B3 were found to be inactive, but the trimeric procyanidin C1 strongly inhibited Na+,K+-ATPase with an IC50 of 4.5 µM. This newly discovered inhibitor was docked into crystal structures mimicking the Na3E1∼P·ADP and K2E2·Pi states to identify potential interaction sites within Na+,K+-ATPase. Possible binding mechanisms and the principle responsible for the observed root extract activity are discussed.

• MeSH
• flavonoidy MeSH
• ionty metabolismus   MeSH
• proantokyanidiny * metabolismus   farmakologie   MeSH
• rostlinné extrakty farmakologie   MeSH
• sodík metabolismus   MeSH
• sodíko-draslíková ATPasa metabolismus   MeSH
• tandemová hmotnostní spektrometrie MeSH
• Viola * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• flavonoidy MeSH
• ionty MeSH
• proantokyanidiny * MeSH
• procyanidin trimer C1 MeSH Prohlížeč
• rostlinné extrakty MeSH
• sodík MeSH
• sodíko-draslíková ATPasa MeSH

We examined the inhibitory effects of three flavonolignans and their dehydro- derivatives, taxifolin and quercetin on the activity of the Na(+)/K(+)-ATPase (NKA). The flavonolignans silychristin, dehydrosilychristin and dehydrosilydianin inhibited NKA with IC50 of 110 ± 40 μM, 38 ± 8 μM, and 36 ± 14 μM, respectively. Using the methods of molecular modeling, we identified several possible binding sites for these species on NKA and proposed the possible mechanisms of inhibition. The binding to the extracellular- or cytoplasmic C-terminal sites can block the transport of cations through the plasma membrane, while the binding on the interface of cytoplasmic domains can inhibit the enzyme allosterically. Fluorescence spectroscopy experiments confirmed the interaction of these three species with the large cytoplasmic segment connecting transmembrane helices 4 and 5 (C45). The flavonolignans are distinct from the cardiac glycosides that are currently used in NKA treatment. Because their binding sites are different, the mechanism of inhibition is different as well as the range of active concentrations, one can expect that these new NKA inhibitors would exhibit also a different biomedical actions than cardiac glycosides.

• Klíčová slova
• Na+/K+-ATPase, binding sites, flavonolignans, inhibition, sodium pump,
• Publikační typ
• časopisecké články MeSH

A set of single-tryptophan mutants of the Na(+)/K(+)-ATPase isolated, large cytoplasmic loop connecting transmembrane helices M4 and M5 (C45) was prepared to monitor effects of the natural cytoplasmic ligands (i.e., Mg(2+) and/or ATP) binding. We introduced a novel method for the monitoring of the changes in the electrostatic surface potential (ESP) induced by ligand binding, using the quenching of the intrinsic tryptophan fluorescence by acrylamide or iodide. This approach opens a new way to understanding the interactions within the proteins. Our experiments revealed that the C45 conformation in the presence of the ATP (without magnesium) substantially differed from the conformation in the presence of Mg(2+) or MgATP or in the absence of any ligand not only in the sense of geometry but also in the sense of the ESP. Notably, the set of ESP-sensitive residues was different from the set of geometry-sensitive residues. Moreover, our data indicate that the effect of the ligand binding is not restricted only to the close environment of the binding site and that the information is in fact transmitted also to the distal parts of the molecule. This property could be important for the communication between the cytoplasmic headpiece and the cation binding sites located within the transmembrane domain.

• MeSH
• adenosintrifosfát metabolismus   farmakologie   MeSH
• akrylamid metabolismus   farmakologie   MeSH
• cytoplazma metabolismus   MeSH
• fluorescence MeSH
• hořčík metabolismus   farmakologie   MeSH
• jodidy metabolismus   farmakologie   MeSH
• konformace proteinů účinky léků   MeSH
• ligandy MeSH
• molekulární modely MeSH
• mutace MeSH
• myši MeSH
• povrchové vlastnosti MeSH
• sodíko-draslíková ATPasa chemie   genetika   metabolismus   MeSH
• statická elektřina * MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• adenosintrifosfát MeSH
• akrylamid MeSH
• hořčík MeSH
• jodidy MeSH
• ligandy MeSH
• sodíko-draslíková ATPasa MeSH