Biospeciation of Potential Vanadium Drugs of Acetylacetonate in the Presence of Proteins

Abstract

Among vanadium compounds with potential medicinal applications, [V IV O(acac) 2 ] is one of the most promising for its antidiabetic and anticancer activity. In the organism, however, interconversion of the oxidation state to +III and +V and binding to proteins are possible. In this report, the transformation of V III (acac) 3 , V IV O(acac) 2 , and V V O 2 (acac) − 2 after the interaction with two model proteins, lysozyme (Lyz) and ubiquitin (Ub), was studied with ESI-MS (ElectroSpray Ionization-Mass Spectroscopy), EPR (Electron Paramagnetic Resonance), and computational (docking) techniques. It was shown that, in the metal concentration range close to that found in the organism (15-250 µM), V III (acac) 3 is oxidized to V IV O(acac) + and V IV O(acac) 2 , which-in their turn-interact with proteins to give n[V IV O(acac)]-Protein and n[V IV O(acac) 2 ]-Protein adducts. Similarly, the complex in the +IV oxidation state, V IV O(acac) 2 , dissociates to the mono-chelated species V IV O(acac) + which binds to Lyz and Ub. Finally, V V O 2 (acac) − 2 undergoes complete dissociation to give the 'bare' V V O + 2 ion that forms adducts n[V V O 2 ]-Protein with n = 1-3. Docking calculations allowed the prediction of the residues involved in the metal binding. The results suggest that only the V IV O complex of acetylacetonate survives in the presence of proteins and that its adducts could be the species responsible of the observed pharmacological activity, suggesting that in these systems V IV O 2+ ion should be used in the design of potential vanadium drugs. If V III or V V O 2 potential active complexes had to be designed, the features of the organic ligand must be adequately modulated to obtain species with high redox and thermodynamic stability to prevent oxidation and dissociation.

Integrated experimental/computational approaches to characterize the systems formed by vanadium with proteins and enzymes

“…27 In general, two types of binding are expected for a VC-protein system: (i) coordinative (or covalent) binding, for which the protein replaces L − or another weak ligand, typically H 2 O, with one or more donor-containing residues, resulting in the formation of binary (V IV O 2+ -protein or V V O 2 + -protein) and ternary (V IV/V OL-protein or V IV/V OL 2 -protein) adducts; 39 and (ii) inert (or non-covalent) binding, in which the intact complex V IV OL 2 /V V O 2 L/V V O 2 L 2 binds only through secondary interactions with accessible groups of the protein surface. [40][41][42] Despite major progress over the last years, the prediction and elucidation of the exact binding mechanism of metal moieties (being naked or complexed ions) is still a challenging question. In addition to X-ray diffraction (XRD), several spectroscopic techniques, such as XANES, XAFS, NMR, EPR, ESEEM, ENDOR, UV-Vis and CD, are routinely applied for the characterization of metal-protein adducts 43,44 and have been widely employed for systems containing the most stable oxidation states of VCs, i.e.…”

“…In a series of recent works based on the multistep combination of ESI-MS, EPR, full DFT and docking, we fully characterized the interaction of several V IV OL 2 (L = dhp, L-mimosinato (mim), maltolato (ma), acetylacetonato (acac), pipemidato ( pip), and 8-hydroxyquinoline-5-sulfonato ligand (hqs) §) with Mb, Ub and Lyz. 40,54,144,145,150 The potential anticancer and antidiabetic [V IV O(dhp) 2 ] § compound 151,152 will be presented as a first showcase for these interactions.…”

“…To obtain a clear speciation profile of this VC in biological medium, ESI-MS and EPR data were collected for [V III (acac) 3 ], [V IV O(acac) 2 ] and [V V O 2 (acac) 2 ] − in aqueous solution as well as in the presence of Ub, Lyz and Mb. 40,144,145 The data were integrated with computational (docking and QM) techniques. In the following paragraphs, the results with Ub will be presented as an illustrative case.…”

“…The ESI-MS spectrum recorded on an aqueous solution containing V III (acac) 3 shows the peaks of [V III (acac) 3 + X] + and, with high intensity, [V IV O(acac) 2 + X] + with X = H or Na. 40 For the binary system H 2 V V O 4 − /Hacac, only the peaks related to…”

BioMetAll: Identifying Metal-Binding Sites in Proteins from Backbone Preorganization

“…19 In those works, we frequently confront with new-to-Nature metal-binding sites, X-ray structures of proteins without a well-defined binding site 20,21 or even putative binding sites of metallodrugs. [22][23][24][25][26][27][28][29] Part of our efforts allowed us to develop a series of docking approaches [30][31][32] that can well reproduce low energy poses of metal-protein complexes. However, such approaches are only viable if good guesses for metal-binding regions are accessible on the first hand.…”