Tuning the interactions of decavanadate with thaumatin, lysozyme, proteinase K and human serum proteins by its coordination to a pentaaquacobalt(ii) complex cation

Abstract

The decavanadate anion, H_xV₁₀O₂₈^(6−x)− (V₁₀), is one of the most studied vanadium polyoxometalate species. In recent decades several works have pointed to its biological relevance coming mainly from its ability to bind to proteins (such as actin, myosin or ion pumps). On the other hand, non-functional binding was observed in several protein crystal structures, where V₁₀ was incorporated “accidentally” resulting from the presence of Na₃VO₄ as a phosphatase inhibitor. In this work we broaden the potential biological applications of V₁₀ by presenting the synthesis and characterization of two decavanadate species where the anion acts as a ligand: (2-hepH)(NH₄)[{Cu(H₂O)₂(2-hep)}₂V₁₀O₂₈]·4H₂O (V₁₀Cu) and (2-hepH)₂[{Co(H₂O)₅}₂V₁₀O₂₈]·4H₂O (V₁₀Co) (2-hep = 2-hydroxyethylpyridine). Unlike free decavanadate, the complex anions stay intact in model buffer solutions (0.1 M 2-(N-morpholino)ethanesulfonic acid, 0.5 M NaCl, pH = 5.8 and 8.0). It has been shown that V₁₀Co is stable also in the presence of proteins and for the first time it was possible to study the interaction of decavanadate with proteins without the interference of lower vanadate oligomers. This allowed comparison of interactions of V₁₀ and V₁₀Co with the model proteins thaumatin, lysozyme, proteinase K, human serum albumin and transferrin under conditions close to biological ones (0.1 M 2-(N-morpholino)ethanesulfonic acid, 0.5 M NaCl, pH = 5.8). The linewidths of the signals at half-height in ⁵¹V NMR spectra reflect the strength of interaction of a vanadium species with a protein, and thus it was shown that V₁₀ and V₁₀Co both bind strongly to thaumatin, V₁₀ binds to lysozyme and V₁₀Co binds to proteinase K. V₁₀ interacts with both human serum albumin and transferrin, but surprisingly V₁₀Co exhibits high affinity to transferrin but does not interact with albumin.