Multiple and Variable Binding of Pharmacologically Active Bis(maltolato)oxidovanadium(IV) to Lysozyme

[Image: see text] The interaction with proteins of metal-based drugs plays a crucial role in their transport, mechanism, and activity. For an active ML(n) complex, where L is the organic carrier, various binding modes (covalent and non-covalent, single or multiple) may occur and several metal moieties (M, ML, ML(2), etc.) may interact with proteins. In this study, we have evaluated the interaction of [V(IV)O(malt)(2)] (bis(maltolato)oxidovanadium(IV) or BMOV, where malt = maltolato, i.e., the common name for 3-hydroxy-2-methyl-4H-pyran-4-onato) with the model protein hen egg white lysozyme (HEWL) by electrospray ionization mass spectrometry, electron paramagnetic resonance, and X-ray crystallography. The multiple binding of different V-containing isomers and enantiomers to different sites of HEWL is observed. The data indicate both non-covalent binding of cis-[VO(malt)(2)(H(2)O)] and [VO(malt)(H(2)O)(3)](+) and covalent binding of [VO(H(2)O)(3–4)](2+) and cis-[VO(malt)(2)] and other V-containing fragments to the side chains of Glu35, Asp48, Asn65, Asp87, and Asp119 and to the C-terminal carboxylate. Our results suggest that the multiple and variable interactions of potential V(IV)OL(2) drugs with proteins can help to better understand their solution chemistry and contribute to define the molecular basis of the mechanism of action of these intriguing molecules.