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

The decavanadate anion, HxV10O28(6-x)- (V-10), 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 V-10 was incorporated accidentally'' resulting from the presence of Na3VO4 as a phosphatase inhibitor. In this work we broaden the potential biological applications of V-10 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)}(2)V10O28]center dot 4H(2)O (V10Cu) and (2-hepH)(2)[{Co(H2O)(5)}(2)V10O28]center dot 4H(2)O (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 V-10 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 V-51 NMR spectra reflect the strength of interaction of a vanadium species with a protein, and thus it was shown that V-10 and V10Co both bind strongly to thaumatin, V-10 binds to lysozyme and V10Co binds to proteinase K. V-10 interacts with both human serum albumin and transferrin, but surprisingly V10Co exhibits high affinity to transferrin but does not interact with albumin.