Interactions of di-imine copper(II) complexes with albumin: competitive equilibria, promoted oxidative damage and DFT studies

Abstract

Interações de alguns compostos di-imínicos de cobre(II) com albumina de soro bovino (BSA) foram investigadas por técnicas espectroscópicas, visando comparar a estabilidade dos complexos e verificar a sua capacidade de causar danos oxidativos à proteína. Os ligantes imínicos tri-e tetradentados utilizados neste trabalho contêm grupamentos piridina, pirazina ou imidazol, frequentemente encontrados no meio biológico. A estabilidade termodinâmica relativa de cada um dos complexos foi determinada através de dicroísmo circular (CD), usando a própria BSA como ligante competitivo. Os valores estimados das constantes de equilíbrio aparentes foram muito semelhantes entre si e ao da espécie Cu(BSA), para a qual log K Cu(BSA) = 12.9 já foi relatado na literatura, mostrando que os complexos estudados são bastante estáveis em condições fisiológicas. Dois diferentes sítios de coordenação do íon cobre foram verificados nestes estudos, evidenciados por medidas espectroscópicas (UV-Vis, CD e EPR), dependendo do ligante e da proporção estequiométrica [CuL]/[BSA] utilizada. Entretanto, a inserção do íon cobre em qualquer dos sítios ligantes ocasionou danos oxidativos significativos à proteína, especialmente em presença de peróxido de hidrogênio, indicando um processo oxidativo com formação de espécies reativas de oxigênio (EROs). Um tripeptídeo amidado, Asp-Thr-His-NH 2 , mimético do sítio N-terminal da BSA, foi sintetizado e a investigação de sua interação com os complexos de cobre permitiu uma compreensão melhor do sistema cobre-BSA. Cálculos de estrutura eletrônica empregando a teoria do funcional de densidade (DFT) foram efetuados para determinar as energias de ligação do cobre em cada complexo e no sítio N-terminal da proteína, buscando correlacioná-las com os dados de estabilidade termodinâmica. Interactions of some diimine copper(II) complexes with bovine serum albumin (BSA) were investigated by spectroscopic techniques in order to compare the stability of the complexes and their capability of causing oxidative damage to the protein. The tri-and tetradentate imine ligands employed in this work contain pyridine, pyrazine or imidazole moieties, which are ubiquitous in biological systems. The relative thermodynamic stabilities of the copper(II) complexes were estimated by circular dichroism (CD) using BSA as the competitive ligand. The apparent stability constants determined for the complexes are very similar to one another and to that of the Cu(BSA) complex itself, for which log K Cu(BSA) = 12.9 has already been described in the literature, indicating that the complexes are quite stable under physiological conditions. Two different copper binding sites were evidenced on BSA by spectroscopic measurements (CD, UV-Vis and EPR), depending on the ligand and on the [CuL]:[protein] stoichiometric ratio. Metal binding to any of the sites gives rise to significant protein oxidative damage, especially in the presence of hydrogen peroxide, indicating an oxidative process based on reactive oxygen species (ROS). A small amidated peptide, As...

Reactivity of dinuclear copper(II) complexes towards melanoma cells: Correlation with its stability, tyrosinase mimicking and nuclease activity

“…The relative stability of the complexes was estimated in titration experiments, using HSA as competitive ligand, in similar procedures already reported [16]. CD spectra were recorded in a JASCO J-720 spectropolarimeter, using a quartz cuvette of 0.1 cm path length, at room temperature, in the range 200-300 nm or 350-650 nm.…”

“…By considering competitive equilibria of copper ions coordinated to each ligand in the studied complexes, or inserted at N-terminal site of HSA, it was achieved an estimation of the apparent stability of complexes 1 and 2, according to procedures already described [16]. Titrations of a protein solution with each copper(II) complex, monitored through CD spectra at the characteristic band at 564 nm, attributed to the insertion of a copper ion at the selective N-terminal metal binding site of the protein [17], were carried out with this purpose.…”

A Robust Analytical Approach for the Identification of Specific Protein Carbonylation Sites: Metal-Catalyzed Oxidations of Human Serum Albumin

“…Human serum albumin is known to bind transition metals at the N-terminus. In addition, His-27, His-91, His-129, His-170, and His-271 also have been reported be metal binding sites for human serum albumin (Bal et al, 1998; Glennon and Sarkar, 1982; Laussac and Sarkar, 1984; Giroux and Schoun, 1981; Rozga et al 2007; Azzellini et al 2010). In the current study, the modifications at Lys-97, Lys-161, Lys-169, Arg-169, and Lys-490 are very close to these reported metal-binding sites.…”

“…HSA is known to bind transition metals and binding sites have been identified near the N-terminus (involving His-27). His-91, His-129, His-130, and His-271 have also been implicated as potential metal binding sites (Azzellini et al 2010; Bal et al, 1998; Giroux and Schoun, 1981; Glennon and Sarkar, 1982; Laussac and Sarkar, 1984; Rozga et al 2007). Here we examine whether protein carbonylation selectivity can be correlated with the known metal binding properties of this model protein.…”

Shedding Light on the Hydrolysis Mechanism of cis, trans-[Ru(dmso)4Cl2] Complexes and Their Interactions with DNA—A Computational Perspective

“…Since the discovery by Rosemberg in 1965 that cisplatin is able to inhibit bacterial cell division, other transition-metal complexes as iron, − ruthenium, and osmium started to be widely studied as potential antitumor agents against different types of cancer cells. ,− …”