Interaction of potential vanadium drugs with proteins studied by an experimental and computational approach

The interaction of potential vanadium drugs with proteins is essential to explain their pharmacological effects in the organism. The binding to blood serum proteins, such as transferrin and albumin, influences the transport toward the target organs and the uptake into the cells, while that to cellular components can stabilize specific species in the cytosol and determine the active species [1]. The study of this interaction is fundamental to get insights on the adducts formed and on type of binding. In the absence of an XRD analysis, spectroscopic (NMR, EPR, ESEEM, ENDOR, UV-Vis and CD spectroscopy) and spectrometric techniques (MS) can provide only partial information on the metal-protein interaction and, over the last years, these were complemented by computational methods. In particular, the docking approach - generally used to treat the non-covalent interactions - was improved in GOLD computer software to take into account the formation of one or more coordination bonds between the metal and protein donors [2,3] and was applied to several metallodrugs [3]. In this work, the interaction of potential drugs VIVOL2, where L is a bidentate anionic ligand such as 1,2-dimethyl-3-hydroxy-4(1H)-pyridinonate, maltolate, acetylacetonate, picolinate, kojate or L-mimosinate [4], with several proteins (for example, lysozyme) was studied by a multistep method based on the combined application of spectrometric (Electron Spray Ionization-MS), spectroscopic (EPR) and computational (docking and QM) techniques. ESIMS allows to determine the number of vanadium moieties bound to protein, EPR to distinguish the type of residues involved in the coordination, docking and full QM models to predict the specific residues involved in the vanadium coordination as well as the threedimensional structure and stabilization of the adducts through hydrogen bonds and/or van der Waals contacts. The results indicate that the formation of adducts with VOL+ and cis-VOL2 moieties is possible. With VOL+ the contemporaneous coordination of two amino acid side-chain donors is expected, while with cis-VOL2 only a monodentate equatorial binding is suggested. The donors involved in the metal coordination belong mainly to histidine, aspartate and glutamate residues. It will be illustrated that this approach is generalizable and could be applied to other metal complexes and proteins, using - depending on the metal features - different spectroscopic techniques.