title: Binding properties of ferrocene-glutathione conjugates as inhibitors and sensors for glutathione S-transferases.
abstract: The binding properties of two electroactive glutathione-ferrocene conjugates that consist in glutathione attached to one or both of the cyclopentadienyl rings of ferrocene (GSFc and GSFcSG), to Schistosoma japonica glutathione S-transferase (SjGST) were studied by spectroscopy fluorescence, isothermal titration calorimetry (ITC) and differential pulse voltammetry (DPV). Such ferrocene conjugates resulted to be competitive inhibitors of glutathione S-transferase with an increased binding affinity relative to the natural substrate glutathione (GSH). We found that the conjugate having two glutathione units (GSFcSG) exhibits an affinity for SjGST approximately two orders of magnitude higher than GSH. Furthermore, it shows negative cooperativity with the affinity for the second binding site two orders of magnitude lower than that for the first one. We propose that the reason for such negative cooperativity is steric since, i) the obtained thermodynamic parameters do not indicate profound conformational changes upon GSFcSG binding and ii) docking studies have shown that, when bound, part of the first bound ligand invades the second site due to its large size. In addition, voltammetric measurements show a strong decrease of the peak current upon binding of ferrocene-glutathione conjugates to SjGST and provide very similar K values than those obtained by ITC. Moreover, the sensing ability, expressed by the sensitivity parameter shows that GSFcSG is much more sensitive than GSFc, for the detection of SjGST.
authors.affiliation: Área de Química Orgánica, Faculty of Experimental Sciences, University of Almería, La Cañada de San Urbano, 04120 Almería, Spain.
authors.forename: Manuel C
authors.initials: MC
authors.lastname: Martos-Maldonado
authors.forename: Juan M
authors.initials: JM
authors.lastname: Casas-Solvas
authors.forename: Ramiro
authors.initials: R
authors.lastname: Téllez-Sanz
authors.forename: Concepción
authors.initials: C
authors.lastname: Mesa-Valle
authors.forename: Indalecio
authors.initials: I
authors.lastname: Quesada-Soriano
authors.forename: Federico
authors.initials: F
authors.lastname: García-Maroto
authors.forename: Antonio
authors.initials: A
authors.lastname: Vargas-Berenguel
authors.forename: Luís
authors.initials: L
authors.lastname: García-Fuentes
mesh_terms: D000818:Animals; D001665:Binding Sites; D015374:Biosensing Techniques / Q000379:methods*; D002151:Calorimetry; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D005296:Ferrous Compounds / Q000737:chemistry*; D005978:Glutathione / Q000737:chemistry*; D005982:Glutathione Transferase / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015801:Helminth Proteins / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000075163:Metallocenes; D008958:Models, Molecular; D011199:Potentiometry; D011485:Protein Binding; D012549:Schistosoma japonicum / Q000201:enzymology*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D004791:Enzyme Inhibitors; D005296:Ferrous Compounds; D015801:Helminth Proteins; D000075163:Metallocenes; D005982:Glutathione Transferase; D005978:Glutathione; C004998:ferrocene