Implications of oxidovanadium(IV) binding to actin

Recent advances into vanadyl, vanadate and decavanadate interactions with actin

“…3) 13 Other studies performed with ferritin described a stoichiometry of 16 vanadyl cations to one protein molecule, 26 this cation being recognized to bind to several proteins, at the same and higher orders of magnitude than the one described for actin. [27][28][29][30] Similarly as it was described above for decavanadate, the presence of ATP in the assay medium prevents the interaction between vanadyl and actin, hence no EPR signals are detected. 13 Recently reviewed decavanadate insights into biological systems have pointed out that this oligovanadate is either more or less efficient than the corresponding simple oxovanadates in targeting proteins, particularly at the nucleotide binding site.…”

“…Although for both vanadyl and decavanadate the inhibition curve contains two behaviours, it was determined that the IC 50 for the inhibition of polymerization reaction was lower for decavanadate by comparison with vanadyl (68 and 300 mM, respectively), whereas no effects were observed up to 2 mM vanadate, as described previously for 8 mM G-actin in the reaction medium. 4,30 Therefore, for a decavanadate : actin ratio of 8.5, decavanadate inhibits polymerization, whereas a vanadyl : actin ratio of 37.5 is needed to induce the same effect.…”

“…The lack of quenching of F-actin intrinsic fluorescence by vanadyl suggests that the tryptophans present in the protein are protected from vanadium effects when the actin is present in its polymerized form. 14,30 Eventually, actin conformational changes induced during actin polymerization prevent the vanadium quenching. However, for higher vanadyl concentrations from 200 to 500 mM, a maximum of 75% intrinsic protein quenching was observed, as described elsewhere.…”

“…14,30 However, many biochemical studies using vanadium complexes and, particularly, decavanadate (with absorptions at 360 and 400 nm 7,31 ), do not take into consideration those effects, which decreases the fluorescence measurements accuracy. For the maximum decavanadate concentration referred to in these studies, 20 mM, (meaning 0.2 mM total vanadium), the absorbance values at excitation and emission wavelengths used in assays (295 and 340 nm, respectively) attain to a sum of 0.841 O.D.…”

“…14,30 Since it is known that the larger the value of the ATP exchange rate, the more available the cleft should be, 38 it can be concluded that vanadyl and decavanadate are clearly promoting structural alterations on actin ATP binding sites.…”