Vanadates form insoluble complexes with histones

Vanadium oxoanions are known to have a variety of physiological effects including insulin-like activity, inhibition of phosphotyrosine phosphatases, as well as direct interactions with a variety of cellular proteins, such as microtubules. In this study, vanadate was found to form insoluble complexes with histones, as well as other positively charged proteins, in a concentration dependent fashion. This interaction occurred over a 0.5-10 mM range which corresponds to the concentration range required for many of vanadate's known physiological effects. Results from precipitation experiments using vanadate solutions with or without the yellow-orange decavanadate indicated that the decamer form is primarily responsible for this precipitation. Vanadate was able to selectively precipitate histones from soluble chromatin as well as from a soluble bacterial protein extract to which a low concentration of histones had been added. Vanadate was also able to effectively precipitate histone from solutions as low as 0.006 mg/mL histone. Thus, the selective precipitation of histones and other positively charged proteins by vanadate can be utilized as a tool for protein purification. In addition, this interaction may provide insight into the mechanisms for the physiological effects of vanadate.