title: Evaluation of the binding of oxovanadium(IV) to human serum albumin.
abstract: 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 Cu(II) and Zn(II) as metal probes. The results show that V(IV)O 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 V(IV)O-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 V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, 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 (V(IV)OL(2))(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 V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Lisbon, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Correia
authors.forename: Tamás
authors.initials: T
authors.lastname: Jakusch
authors.forename: Enoch
authors.initials: E
authors.lastname: Cobbinna
authors.forename: Sameena
authors.initials: S
authors.lastname: Mehtab
authors.forename: Isabel
authors.initials: I
authors.lastname: Tomaz
authors.forename: Nóra V
authors.initials: NV
authors.lastname: Nagy
authors.forename: Antal
authors.initials: A
authors.lastname: Rockenbauer
authors.forename: João Costa
authors.initials: JC
authors.lastname: Pessoa
authors.forename: Tamás
authors.initials: T
authors.lastname: Kiss
mesh_terms: D001667:Binding, Competitive; D040761:Biomimetic Materials / Q000378:metabolism*; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism*; D013696:Temperature; D014638:Vanadates / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
chemical_list: D012709:Serum Albumin; C075743:oxovanadium IV; D014638:Vanadates; D003300:Copper; D015032:Zinc