Rutao Liu

New Insights into the Behavior of Bovine Serum Albumin Adsorbed onto Carbon Nanotubes: Comprehensive Spectroscopic Studies

Bovine serum albumin (BSA) nonspecifically binds to well-dispersed multiwalled carbon nanotubes (MWCNTs), forming a stable bioconjugate. After accounting for the inner filter effect, we found the fluorescence intensity of BSA was quenched by MWCNTs in static mode, which was authenticated by lifetime measurements and Stern-Volmer calculations. The thermodynamic parameters DeltaG(o), DeltaS(o), and DeltaH(o) were -9.67 x 10(3) + 2.48 x 10(3) ln lambda J x mol(-1), 41.0 - 0.828 ln lambda J x mol(-1) x K(-1), and 7.30 x 10(3) + 2.23 x 10(3) ln lambda J x mol(-1) (lambda < 1 x 10(-4)), respectively, which shows a spontaneous and electrostatic interaction. Scatchard analysis and UV-visible results provide statistical data concerning changes in the microenvironment of amide moieties in response to different doses of MWCNTs, revealing different behavior of the BSA molecules. The absorption spectra also show that the tertiary structure of the protein was partially destroyed. The content of secondary structure elements of BSA was changed by the tubes. This work elucidates the interaction mechanism of BSA and MWCNTs from a spectroscopic angle.

Phenotypic Characterization of the Binding of Tetracycline to Human Serum Albumin

Because of the widely usage of the veterinary drug tetracycline (TC), its residue exist extensively in the environment (e.g., animal food, soils, surface water, and groundwater) and can enter human body, being potential harmful. Human serum albumin (HSA) is a major transporter for endogenous and exogenous compounds in vivo. The aim of this study was to examine the interaction of HSA with TC through spectroscopic and molecular modeling methods. The inner filter effect was eliminated to get accurate binding parameters. The site marker competition experiments revealed that TC binds to site II (subdomain IIIA) of HSA mainly through electrostatic interaction, illustrated by the calculated negative ΔH° and ΔS°. Furthermore, molecular docking was applied to define the specific binding sites, the results of which show that TC mainly interacts with the positively charged amino acid residues Arg 410 and Lys 414 predominately through electrostatic force, in accordance with the conclusion of thermodynamic analysis. The binding of TC can cause conformational and some microenvironmental changes of HSA, revealed by UV-visible absorption, synchronous fluorescence, and circular dichroism (CD) results. The accurate and full basic data in the work is beneficial to clarifying the binding mechanism of TC with HSA in vivo and understanding its effect on protein function during the blood transportation process.

Characterizing the Interaction between Tartrazine and Two Serum Albumins by a Hybrid Spectroscopic Approach

Tartrazine is an artificial azo dye commonly used in food products. The present study evaluated the interaction of tartrazine with two serum albumins (SAs), human serum albumin (HSA) and bovine serum albumin (BSA), under physiological conditions by means of fluorescence, three-dimensional fluorescence, UV-vis absorption, and circular dichroism (CD) techniques. The fluorescence data showed that tartrazine could bind to the two SAs to form a complex. The binding process was a spontaneous molecular interaction procedure, in which van der Waals and hydrogen bond interactions played a major role. Additionally, as shown by the UV-vis absorption, three-dimensional fluorescence, and CD results, tartrazine could lead to conformational and some microenvironmental changes of both SAs, which may affect the physiological functions of SAs. The work provides important insight into the mechanism of toxicity of tartrazine in vivo.

New strategy for the evaluation of CdTe quantum dot toxicity targeted to bovine serum albumin

The biological toxicity of CdTe quantum dots (QDs) to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by CdTe QDs was a static quenching process and the binding constant is 6.05x10(3) and the number of binding sites is 0.7938. The thermodynamic parameters (DeltaH=-62.33 kJ mol(-1), DeltaG=-21.21 kJ mol(-1), and DeltaS=-140.3 J mol(-1) s(-1)) indicate that hydrogen bonds and van der Waals forces between the protein and the QDs are the main binding forces stabilizing the complex. In addition, UV-vis and CD results showed that the addition of CdTe QDs changed the conformation of BSA.

Binding of oxytetracycline to bovine serum albumin: spectroscopic and molecular modeling investigations.

The residue of the widely used veterinary drug oxytetracycline (OTC) in the environment (e.g., animal food, soils, surface water, and groundwater) is potentially harmful. Knowledge of its binding to proteins contributes to the understanding of its toxicity in vivo. This work establishes the binding mode of OTC with bovine serum albumin (BSA) under physiological conditions by spectroscopic methods and molecular modeling techniques. The inner filter effect was eliminated to get accurate data (binding parameters). On the basis of the thermodynamic results and site marker competition experiments, it was considered that OTC binds to site II (subdomain IIIA) of BSA mainly by electrostatic interaction. Furthermore, using the BSA model established with CPHmodels, molecular docking and some other molecular modeling methods were applied to further define that OTC interacts with the Arg 433, Arg 436, Ala 429, and Pro 516 residues of BSA. In addition, UV-visible absorption, synchronous fluorescence, and circular dichroism (CD) results showed that the binding of OTC can cause conformational and some microenvironmental changes of BSA. The work provides accurate and full basic data for clarifying the binding mechanisms of OTC with BSA in vivo and is helpful for understanding its effect on protein function during its transportation and distribution in blood.

The interaction between Ag+ and bovine serum albumin: a spectroscopic investigation.

By using spectroscopic methods, we probed the interaction of Ag(+) with bovine serum albumin (BSA) in an aqueous environment. Fluorescence of BSA quenched by Ag(+) is a dynamic quenching process. Two binding modes-a strong one at low concentration of Ag(+) and a weak one at high concentration were found. The association constant (K(A)) and the number of binding sites (n) were 4.88×10(3)M(-1) and 1.17 for strong binding, and 17.6M(-1) and 0.547 for weak binding at 293K. The results of thermodynamic parameters ΔH(θ), ΔG(θ) and ΔS(θ) for instinct binding modes at different temperatures indicated that the hydrogen bonding and van der Waals interaction play a major role for low Ag(+)/BSA ratio while electrostatic association for high Ag(+)/BSA ratio. Data of UV-Vis and Circular dichroism (CD) suggested that with the increasing amount of Ag(+), the secondary structure undergoes a decrease in α-helix and an increase in β content and the backbone of BSA experiences a micro-environmental alteration. Furthermore, the distance r between donor (Trp-212) and acceptor (Ag(+)) was evaluated to be 10nm according to nonradiative energy transfer theory.

Binding of Sudan II and Sudan IV to bovine serum albumin: Comparison studies

In this paper, we report the interaction of Sudan II and Sudan IV to bovine serum albumin (BSA). Structural analysis showed that both Sudan II and Sudan IV interact mainly with BSA at the hydrophobic pocket and via Van der Waals forces. The number of bound Sudan molecule for each protein molecule was approximately 1. The overall binding constants at 293 K (20°C) estimated for Sudan II and Sudan IV were 1.22 × 10(4)M(-1) and 1.48 × 10(4)M(-1), respectively. BSA backbone structure was damaged by the dyes with more severe phenomenon observed for Sudan IV. For two Sudan dyes with the same concentration, Sudan IV could cause more alterations on CD spectra of BSA with slight decrease of α-helical content and increase of β-sheet content, suggesting a partial protein unfolding.

Noncovalent interaction of oxytetracycline with the enzyme trypsin.

Oxytetracycline (OTC) is a kind of widely used veterinary drugs. The residue of OTC in the environment (e.g., animal food, soils, surface, and groundwater) is potentially harmful. In this article, the binding mode of OTC with trypsin was investigated using spectroscopic and molecular docking methods. OTC can interact with trypsin with one binding site to form OTC-trypsin complex, resulting in inhibition of trypsin activity and change of the secondary structure and the microenvironment of the tryptophan residues of trypsin. After elimination of the inner filter effect, the association constant, K, was calculated to be K(290K) = 1.36 × 10(5) L mol(-1), K(298K) = 7.30 × 10(4) L mol(-1), and K(307K) = 3.58 × 10(4) L mol(-1) at three different temperatures. The calculated thermodynamic parameters (negative values of ΔH(○) and ΔS(○)) indicated that van der Waals interactions and hydrogen bonds play a major role during the interaction. The molecular docking study revealed that OTC bound into the S1 binding pocket, which illustrates that the trypsin activity was competitively inhibited by OTC, in accordance with the conclusion of the trypsin activity experiment. This work establishes a new strategy to probe the toxicity of OTC and contributes to clarify its molecular mechanism of toxicity in vivo. The combination of spectroscopic and molecular docking methods in this work can be applied to investigate the potential enzyme toxicity of other small organic pollutants and drugs.

Impact of carbon chain length on binding of perfluoroalkyl acids to bovine serum albumin determined by spectroscopic methods.

Perfluoroalkyl acids (PFAAs), an emerging class of globally environmental contaminants, pose a great threat to humans with wide exposure from food and other potential sources. To evaluate the toxicity of PFAAs at the protein level, the effects of three PFAAs on bovine serum albumin (BSA) were characterized by fluorescence spectroscopy, synchronous fluorescence spectroscopy, and circular dichroism (CD). On the basis of the fluorescence spectra and CD data, we concluded that perfluoropentanoic acid (PFPA) had little effect on BSA. However, perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) exhibited remarkable fluorescence quenching, which was attributed to the formation of a moderately strong complex. The enthalpy change (DeltaH) and entropy change (DeltaS) indicated that van der Waals forces and hydrogen bonds were the dominant intermolecular forces in the binding of PFAAs to BSA. Furthermore, the BSA conformation was slightly altered in the presence of PFOA and PFDA, with a reduction of alpha helix. These results indicated that PFAAs indeed impact the conformation of BSA, and PFAAs with longer carbon chains were more toxic, especially at lower concentrations.

Toxic interaction mechanism between oxytetracycline and bovine hemoglobin

Oxytetracycline (OTC) is a kind of widely used veterinary drugs. The residue of OTC in the environment is potentially harmful. In the present work, the interaction between OTC and bovine hemoglobin (BHb) was investigated by fluorescence, synchronous fluorescence, UV-vis absorption, circular dichroism and molecular modeling techniques under physiological conditions. The experimental results showed that OTC can bind with BHb to form complex. The binding process is a spontaneous molecular interaction procedure, in which van der Waals and hydrogen bonds interaction play a major role. The number of binding sites were calculated to be 1.12 (296 K), 1.07 (301 K) and 0.95 (308 K), and the binding constants were of K(296 K)=9.43 x 10(4) Lmol(-1), K(301 K)=4.56 x 10(4) Lmol(-1) and K(308 K)=1.12 x 10(4) Lmol(-1) at three different temperatures. Based on the Förster theory of nonradiative energy transfer, the binding distance between OTC and the inner tryptophan residues of BHb was determined to be 2.37 nm. The results of UV-vis absorption, synchronous fluorescence and CD spectra indicated that OTC can lead to conformational and some microenvironmental changes of BHb, which may affect physiological functions of hemoglobin. The synchronous fluorescence experiment revealed that OTC binds into hemoglobin central cavity, which was verified by molecular modeling study. The work is helpful for clarifying the molecular toxic mechanism of OTC in vivo.