Unveiling VIVO2+ Binding Modes to Human Serum Albumins by an Integrated Spectroscopic–Computational Approach

Human serum albumin (HSA) is involved in the transport of metal ions and potential metallodrugs. Depending on the metal, several sites are available, among which are N-terminal (NTS) and multi-metal binding sites (MBS). Despite the large number of X-ray determinations for albumins, only one structure with Zn²⁺ is available. In this work, the binding to HSA of the V^IVO²⁺ ion was studied by an integrated approach based on spectroscopic and computational methods, which allowed the systems to be characterized even in the absence of X-ray analysis. The behavior depends on the type of albumin, defatted (HSA^d) or fatted (HSA^f). With HSA^d ‘primary’ and ‘secondary’ sites were revealed, NTS with (His3, His9, Asp13, Asp255) and MBS with (His67, His247, Asp249, Asn99 or H₂O); with increasing the ratio V^IVO²⁺/HSA^d, ‘tertiary’ sites, with one His-N and other donors (Asp/Glu-O or carbonyl-O) are populated. With HSA^f, fatty acids (FAs) cause a rotation of the subdomains IA and IIA, which results in the formation of a dinuclear ferromagnetic adduct (V^IVO)₂^D(HSA^f) with a μ_1,1-Asp249 and the binding of His247, Glu100, Glu252, and His67 or Asn99. FAs hinder also the binding of V^IVO²⁺ to the MBS.