Abstract
Lead is a potent environmental toxin that has accumulated above its natural level as a result of human activity. Pb cation shows major affinity towards protein complexation and it has been used as modulator of protein-membrane interactions. We located the binding sites of Pb(II) with human serum (HSA) and bovine serum albumins (BSA) at physiological conditions, using constant protein concentration and various Pb contents. FTIR, UV-visible, CD, fluorescence and X-ray photoelectron spectroscopic (XPS) methods were used to analyse Pb binding sites, the binding constant and the effect of metal ion complexation on HSA and BSA stability and conformations. Structural analysis showed that Pb binds strongly to HSA and BSA via hydrophilic contacts with overall binding constants of KPb-HSA = 8.2 (±0.8)×104 M−1 and KPb-BSA = 7.5 (±0.7)×104 M−1. The number of bound Pb cation per protein is 0.7 per HSA and BSA complexes. XPS located the binding sites of Pb cation with protein N and O atoms. Pb complexation alters protein conformation by a major reduction of α-helix from 57% (free HSA) to 48% (metal-complex) and 63% (free BSA) to 52% (metal-complex) inducing a partial protein destabilization.
Highlights
Pb is a potent environmental toxin that has accumulated 1000fold above its natural level as a result of human activity [1]
To better understand the interaction of Pb with proteins it was of interest to study the complexation of Pb with well known model proteins such as human and bovine serum albumins and determine Pb binding sites and the effect of metal ion interaction on protein structures in aqueous solution
We present spectroscopic analysis and X-ray photoelectron spectroscopic (XPS) study of the interaction of Pb(II) with human serum albumin (HSA) and bovine serum albumins (BSA) in aqueous solution at physiological conditions, using constant protein concentration and various metal ion contents
Summary
Pb is a potent environmental toxin that has accumulated 1000fold above its natural level as a result of human activity [1]. Even though the deadly effects of lead on human health have been known for many years, the molecular mechanism of Pb toxicity is poorly understood. It is known that Pb cation mimics the effects of Ca and Zn at specific molecular targets [2,3]. Lead toxicity has multifunctional effects on both in vivo and in vitro photosynthetic CO2 fixation and long term exposure results in reduced leaf growth, decreased level of photosynthetic pigments, altered chloroplast structure and decreased enzymatic activity of CO2 assimilation [4,5]. To better understand the interaction of Pb with proteins it was of interest to study the complexation of Pb with well known model proteins such as human and bovine serum albumins and determine Pb binding sites and the effect of metal ion interaction on protein structures in aqueous solution
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