Characterization of interactions between organotin compounds and human serum albumin by capillary electrophoresis coupled with inductively coupled plasma mass spectrometry

Abstract

Inductively coupled plasma mass spectrometry Human serum albumin Affinity capillary electrophoresis Nonequilibrium capillary electrophoresis assays of equilibrium mixtures assays a b s t r a c t Thermodynamic data such as the binding constants are vital parameters describing interactions between exotic trace compounds and biomolecules in biochemical property modeling. In this study, the stability constants of organometallic compound and protein complexes were studied by using capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS), considering its low detection limits and low sample demand. Four organotin compounds (trimethyltin (TMT), tripropyltin (TPrT), tributyltin (TBT), triphenyltin (TPhT)) and human serum albumin (HSA) were used as model organometallic compounds and protein, respectively. Affinity capillary electrophoresis (ACE) and nonequilibrium capillary electrophoresis assays of equilibrium mixtures (NECEEM) were performed and compared by using ICP-MS as the detector to determine the binding constants of organotin compounds and HSA in 1:1 molar ratio assumption. Constant measurements of the two methods were both simple, however, ACE assays were more accurate and more appropriate for the constant determination of the organotin-HSA complexes, considering the errors of the NECEEM method. A good precision of the binding constants (log K b ) using the ACE method was proved by different mathematical calculations, and the values were 6.13 ± 0.51 (TMT), 5.72 ± 0.38 (TPrT), 5.68 ± 0.34 (TBT), 6.05 ± 0.38 (TPhT) respectively for each of the organotin-HSA complexes, showing non-covalent interaction between organotin compounds and HSA. Meanwhile, this study also confirms the suitability of CE-ICP-MS method for further studies on organometallic complexation.

Separative techniques for metalloproteomics require balance between separation and perturbation

“…The composition can therefore theoretically be chosen not to interfere with the metal speciation (which implies the knowledge of the binding constants of metals with all the constituents) or to reflect as closely as possible the medium being studied. As a consequence, many studies were performed using a pH of 7.4, close to the physiological pH, in SEC [38,39,43,48,53,56] or CE [29,32,37,57].…”

“…This phenomenon was exploited in CE (NECEEM: non-equilibrium CE of equilibrium mixtures) to obtain both thermodynamic and kinetic data in a single experiment, as exemplified by the complexation of organotin compounds by human serum albumin [32].…”

“…Moreover, methods requiring long separation columns for technical or analytical reasons negatively impact the relative abundance of metallic complexes. This is often the case with commercial CE instruments, which often require the use of long capillaries (>60 cm) to be coupled with external detectors [29][30][31][32]37,48]. Moreover, lack of selectivity between the various proteins imposes the use of longer columns to increase the resolution.…”

Recent Advances in Affinity Capillary Electrophoresis for Binding Studies

“…It has high efficiency and sensitivity to detect all metals in very small concentrations and can also detect several nonmetals. Coupling ACE-ICP-MS provide low detection limits and particularly small sample sizes [89]. This coupling requires a specific interface to ensure the lock of the CE electric circuit and to regulate the flow rate in the outlet of the electrophoresis to be suitable for the inlet of the detector [90].…”

Capillary Electrophoresis for Quantitative Studies of Biomolecular Interactions

“…83 Following the optimization of experimental conditions the interaction between four organotin compounds (trimethyltin, tripropyltin, tributyltin, triphenyltin) and HSA was investigated. Comparative sets of 11 ACE and NECEEM experiments were carried out withe ICP-MS as a detector.…”