Decavanadate as a biochemical tool in the elucidation of muscle contraction regulation

Recently reported decameric vanadate (V10) high affinity binding site in myosin S1, suggests that it can be used as a tool in the muscle contraction regulation. In the present article, it is shown that V10 species induces myosin S1 cleavage, upon irradiation, at the 23 and 74 kDa sites, the latter being prevented by actin and the former blocked by the presence of ATP. Identical cleavage patterns were found for meta- and decavanadate solutions, indicating that V10 and tetrameric vanadate (V4) have the same binding sites in myosin S1. Concentrations as low as 50 lM decavanadate (5 lM V10 species) induces 30% of protein cleavage, whereas 500 lM metavanadate is needed to attain the same extent of cleavage. After irradiation, V10 species is rapidly decomposed, upon protein addition, forming vanadyl (V4+) species during the process. It was also observed by NMR line broadening experiments that, V10 competes with V4 for the myosin S1 binding sites, having a higher affinity. In addition, V4 interaction with myosin S1 is highly affected by the products release during ATP hydrolysis in the presence or absence of actin, whereas V10 appears to be affected at a much lower extent. From these results it is proposed that the binding of vanadate oligomers to myosin S1 at the phosphate loop (23 kDa site) is probably the cause of the actin stimulated myosin ATPase inhibition by the prevention of ATP/ADP exchange, and that this interaction is favoured for higher vanadate anions, such as V10