Secondary Structure Of BSA Research Articles

In vitro cytotoxicity studies of palladacyclic complexes containing the symmetric diphosphine bridging ligand. Studies of their interactions with DNA and BSA

The reactions between [Pd2{(C,N)–C6H4CH2NH(Et)}2(μ-X)2] (X = Cl or Br) and 1,2-bis(diphenylphosphino)ethane (dppe) in the 1:1 molar ratio resulted in the dppe-bridged Pd(II) complexes, [Pd2{(C,N)–C6H4CH2NH(Et)}2(μ-dppe)(Cl)2] (1) and [Pd2{(C,N)–C6H4CH2NH(Et)}2(μ-dppe)(Br)2] (2), respectively, which were characterized by elemental analyses, infrared (IR), 1H- and 31P{1H} NMR spectroscopy. The molecular structure of 1 was determined by single-crystal X-ray diffraction. In vitro cytotoxicity of 1, 2, dppe, PhCH2NH(Et) and cisplatin were carried out against four human tumor cell lines. The interactions of complexes towards DNA and protein are investigated. The results suggested that both complexes could interact with FS-DNA through the intercalation mode. Moreover, the reactivity towards BSA revealed that the microenvironment and the secondary structure of BSA were changed in the presence of Pd(II) complexes.

Experimental and molecular modeling studies on the interaction of the Ru(II)-piroxicam with DNA and BSA

A mononuclear Ru(II) complex containing two piroxicam (Pir−) ligands was synthesized and fully characterized. Interaction studies of the Pir− anion and the Ru(II) complex with DNA and BSA were carried out using spectroscopic techniques. The results suggested that the Pir− anion binds to DNA in a moderately strong fashion via intercalation between the base stacks of double–stranded DNA, while the Ru(II) complex is a groove binder and interacts with DNA with more affinity. Moreover, the results demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of Pir‾ and Ru(II) complex. The free Pir‾ ligand and the Ru(II) complex can lead to the photocleavage of DNA supercoiled pUC57. Finally, the binding of the Ru(II) complex to BSA and DNA was modeled by molecular docking and molecular dynamic simulation methods.

Chitosan–bovine serum albumin complex formation: A model to design an enzyme isolation method by polyelectrolyte precipitation

Interactions between a model protein (bovine serum albumin—BSA) and the cationic polyelectrolyte, chitosan (Chi), have been characterized by turbidimetry, circular dichroism and fluorescence spectroscopy. It has been found that the conformation of the BSA does not change significantly during the chain interaction between BSA and chitosan forming the non-covalently linked complex. The effects of pH, ionic strength and anions which modify the water structure around BSA were evaluated in the chitosan–BSA complex formation. A net coulombic interaction force between BSA and Chi was found as the insoluble complex formation decreased after the addition of NaCl. Around 80% of the BSA in solution precipitates with the Chi addition. A concentration of 0.05% (w/v) Chi was necessary to precipitate the protein, with a stoichiometry of 6.9 g BSA/g Chi. No modification of the tertiary and secondary structure of BSA was observed when the precipitate was dissolved by changing the pH of the medium. Chitosan proved to be a useful framework to isolate proteins with a slightly acid isoelectrical pH by means of precipitation.

A steady‐state and time‐resolved fluorescence, circular dichroism study on the binding of myricetin to bovine serum albumin

The binding mechanism of myricetin (Myr) to bovine serum albumin was investigated by using steady-state and time-resolved fluorescence and circular dichroism. The results of the steady-state fluorescence quenching experiment indicate that it is a static quenching process (C(Myr)/C(BSA) < or = 3) at low quencher concentration and the binding site is located near the Trp212 residue. The association constants at the different temperatures were calculated. From the thermodynamic parameters, enthalpy change (DeltaH(0)), Gibbs free energy change (DeltaG(0)) and entropy change (DeltaS(0)) obtained in the experiment, it was found that hydrophobic and electrostatic interactions play important roles in binding Myr to BSA. According to the Föster energy transfer theory, the separation distance, r, the energy transfer efficiency, E, and Föster radius, R(0), were calculated. The results obtained from the above experiments indicate that Myr can be tightly bound to BSA. Then, the effects of ionic strength, metal ion, pH and surfactants on the binding Myr and BSA were investigated, which also showed that electrostatic and hydrophobic interactions play a major role in the association process. On the other hand, the conformation and secondary structure of BSA were further studied through circular dichroism and fluorescence synchronous spectra. It was found that the conformation and secondary structure of BSA had also changed after interaction with Myr. The time-resolved fluorescence study showed that the short lifetime of BSA decreased after the addition of Myr, which implies that the buried Trp 212 is the main binding site.

Alkali-induced conformational transition in different domains of bovine serum albumin.

Alkaline pH induced conformational changes in different domains of bovine serum albumin were studied by using domain specific ligands: chloroform, bilirubin and diazepam for domains I, II and III respectively. The effect of alkaline pH on the secondary structure of BSA was monitored by far-UV CD in the range 250 nm to 200 nm. The pH profiles of BSA in the alkaline region showed a two-step change, one corresponding to N<-->B transition (pH 7.5 to 9.0) and the other to B --> U (pH 11.0 to 13.5). Binding of chloroform decreased continuously on increasing pH, whereas binding of diazepam, remained unchanged up to pH 9 and decreased thereafter. In contrast, binding of bilirubin gradually increased up to pH 11.0 and decreased thereafter reaching a value similar to one obtained with native BSA at pH 11.5. Above pH 11.5, bilirubin binding decreased and was abolished completely at pH 12.5. In the pH region 7.5 to 11.0, a continuous decrease in chloroform binding (pH 7.5 to 9.5) and a late decrease in diazepam binding (pH 9.5 to 11.0) suggested major loss of native conformation of domain I followed by domain III during alkaline induced unfolding of BSA. However, a significant increase in bilirubin binding showed a favorable conformational rearrangement in domain II in this pH region (pH7.5 to 11.0). Further, a nearly complete abolishment of bilirubin binding to BSA and significant loss of secondary structure around pH 12.5 indicated that domain II was more resistant to alkaline pH and unfolds only at extreme alkalinity. Taken together, these data suggest that unfolding of three domains of BSA follow the following order of susceptibility towards alkaline denaturation of BSA domain I>domain III>domain II.

Protein-Drug Interaction in the Nanocomposites Prepared by UV and IR Pulsed Laser Deposition

ABSTRACTProtein (bovine serum albumin; BSA)-drug (indomethacin; IM) nanocomposites were prepared by pulsed laser deposition (PLD) at two wavelengths, infrared (1064nm) and ultraviolet (266nm), from uniformly dispersed mixture of BSA and IM as a target. Composite particulates under 50nm were obtained with the coexistence of larger agglomerates over 200nm. Primary structure of BSA is preserved after laser irradiation by both wavelengths. Effects of electronic and vibrational excitation by UV and IR laser respectively on the secondary structure of the nanocomposites were examined by Fourier transform infrared spectroscopy (FT-IR). Chemical shift towards lower wavenumber and a broadening of the amide I band due to PLD treatment were observed by FT-IR. From curve fitting of the amide I into five components, we found the decrease in the ratio of α-helical / β-sheet components with increasing the laser fluence. The secondary structure of BSA is more sensitive to the laser fluence than the wavelength.

Induction of changes in the secondary structure of globular proteins by a hydrophobic surface.

Circular dichroism, ellipsometry and radiolabeling techniques were employed to study the induction of changes in the secondary structure of BSA, myoglobin and cytochrome C by a hydrophobic surface. The results showed that adsorbed protein molecules lose their ordered native structure in the initial stage of adsorption and the structure appears to be a random or disordered conformation. Protein molecules adsorbed in later stages adopt a more ordered secondary structure (alpha helix and beta structure). The changes of secondary structure of globular proteins induced by a hydrophobic surface can be explained by the steric interaction between adsorbed proteins as well as by hydrophobic interactions during the adsorption process. In addition, there is obviously an intermediate stage in which the protein molecules are mainly in the beta structure, indicating that for certain proteins, the beta structure may be a more stable secondary structure than alpha helix on the hydrophobic surface.