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Issue 21, 2012
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Evaluation of the binding of oxovanadium(IV) to human serum albumin

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The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(IV) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using CuII and ZnII as metal probes. The results show that VIVO occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting VIVO–HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of VIVO to bind albumin. The possibility and importance of ternary complex formation between VIVO, HSA and several drug candidates – maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO–HSA–maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (VIVOL2)n(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction VIVOL2 + HSA ⇆ VIVOL2(HSA) is hpno > pic ≥ mal > dhp. (VIVOL)n(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (VIVOL2)n(HSA) species the protein bounds to vanadium through the histidine side chains.

Graphical abstract: Evaluation of the binding of oxovanadium(iv) to human serum albumin

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Publication details

The article was received on 16 Nov 2011, accepted on 02 Mar 2012 and first published on 05 Apr 2012

Article type: Paper
DOI: 10.1039/C2DT12193J
Citation: Dalton Trans., 2012,41, 6477-6487
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    Evaluation of the binding of oxovanadium(IV) to human serum albumin

    I. Correia, T. Jakusch, E. Cobbinna, S. Mehtab, I. Tomaz, N. V. Nagy, A. Rockenbauer, J. Costa Pessoa and T. Kiss, Dalton Trans., 2012, 41, 6477
    DOI: 10.1039/C2DT12193J

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