Characterization of spin-labelled fatty acids and hematoporphyrin binding sites interactions in serum albumin (original) (raw)
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Deciphering the binding modes of hematoporphyrin to bovine serum albumin
Indian Journal of Biochemistry Biophysics, 2014
Interaction of proteins with small molecules is important in understanding delivery and transport of different therapeutic agents, including drugs. In the present study, we investigated the interaction between hematoporphyrin (HP), the principal component of photosensitizing drug with bovine serum albumin (BSA) in aqueous buffer solution using UV-Vis absorption spectroscopy and fluorescence measurements. The results were further substantiated by molecular docking and molecular dynamics (MD) simulation. Our results revealed that fluorescence of BSA was dominantly quenched by the ground-state complex formation with HP accompanied by the electronic energy transfer (EET) to the later. We experimentally determined the thermodynamic parameters such as ∆G 0 , ∆H 0 , and ∆S 0 for the HP-BSA system which were -35.5 kJ mole -1 , -56.4 kJ mole -1 and -0.06 kJ mole -1 K -1 , respectively. These parameters suggested hydrogen-bonding and Van der Waals forces playing major role in the complexation. This was also supported by the binding energy parameters calculated by molecular docking. Moreover, the experimentally determined ∆G 0 nicely correlated with those determined by molecular docking and MD-simulation. Further, computational results clearly showed that the binding of HP with BSA in the subdomains IB and IIA.
Magnetic Resonance Imaging, 1996
The interaction of Fe(II1) and Mn( III) complexes of TPPSI with bovine serum albumin (BSA) was studied by Tl relaxation measurements of water protons and high resolution 'H NMR of the porphyrin moieties. At excess of BSA, both metalloporphyrins bind to BSA as the high spin monomers. The relaxivity of bound MnTPPS, is significantly higher as compared to the free form in solution. When metalloporphyrins are in excess, they aggregate at the BSA surface, up to two MnTPP$, and up to lo-15 FeTPP& units per BSA globule. Bound aggregates are unable to enhance magnetic relaxation of water protons due to the antiferromagnetic coupling between metal ions in the aggregates. Therefore, the dose-effect dependences for metalloporphyrins in the range of metalloporphyrin/BSA ratio of 0 to 25 at the constant BSA concentration at pH 7.4 are characterized by a local maximum at about 2 for MnTPP&, and a global maximum at about 3 for FeTPP$. MnTPP& complex is more effective than FeTPPS, in the whole concentration range. It is suggested that the difference in binding and aggregation properties of metalloporphyrins may be relevant to their relaxation efficiency in vivo, blood transport, and biodistribution.
The Interaction of New Pyridylporphyrins with Bovine Serum Albumin
Russian Journal of Bioorganic …, 2004
The interaction of meso-tetra(4-N-hydroxyethylpyridyl)porphyrin, meso-tetra(3-N-hydroxyethylpyridyl)porphyrin, and their zinc complexes with bovine serum albumin (BSA) was studied by electronic spectroscopy, CD, and equilibrium dialysis at pH 7.2. The titration of the porphyrins with BSA was accompanied by a decrease in light absorption and a bathochromic shift of the Soret band, as well as by the appearance of an isobestic point. The porphyrin interaction with BSA also led to the induction of positive CD spectra in the visible region, which is explained by the porphyrin sorption on the protein globule. The equilibrium dialysis helped in determining the stoichiometry of binding and the binding constants of the porphyrins under study with BSA using Scatchard plots. This interaction is nonspecific and reversible.
Brazilian Journal of Physics, 2006
Electron paramagnetic resonance (EPR) has been used to monitor the interaction of bovine serum albumin (BSA) with cationic cethyltrimethylammonium chloride (CTAC) at pH 7.0. EPR results using 5-DSA and 16-DSA nitroxide spin labels show that in the presence of BSA the EPR spectra are composed of two label populations, one contacting the protein and a second one due to label localization in the micelles. Evidence is also obtained for a competition of the surfactants with the spin labels for the high affinity binding sites of the stearic acid spin labels as monitored by changes in the fraction of the two label populations as the surfactant concentration is increased. The effect of sodium dodecylsulfate (SDS) reported previously seems to be stronger in the sense that increase in SDS concentration leads to a complete transfer of spin label from close protein contact sites to the micelles while for CTAC, apparently, a significant immobilization of probe remains even at higher surfactant concentrations. EPR gives information on the dynamics inside the protein-surfactant aggregates and associated to label localization and motion. The dynamics of the nitroxide spin-labels bound to the protein correlate to the stronger binding of SDS to BSA as compared to CTAC binding. Simulation of EPR spectra for spin labels in pure CTAC micelles, in pure protein or in protein-bound micelles show rotational correlation times similar to those obtained from the simple evaluation based on the intensities of nitrogen hyperfine coupling components. Rotational correlation times obtained for 5-DSA bound to protein are larger as compared to 16-DSA values suggesting greater mobility for the later even when bound to the protein.
Journal of Fluorescence, 2008
The interaction between a free-base, anionic watersoluble porphyrin, TSPP, and the drug carrier protein, bovine serum albumin (BSA) has been studied by time-resolved fluorescence anisotropy (TRFA) and fluorescence correlation spectroscopy (FCS) at two different pH-values. Both rotational correlation times and translational diffusion times of the fluorescent species indicate that TSPP binding to albumin induces very little conformational changes in the protein under physiological conditions. By contrast, at low pH, a biexponential decay is obtained where a short rotational correlation time (7 int =1.2 ns) is obtained, which is likely associated to wobbling movement of the porphyrin in the protein binding site. These physical changes are corroborated by circular dichroism (CD) data which show a 37% loss in the protein helicity upon acidification of the medium. In the presence of excess porphyrin formation of porphyrin Jaggregates is induced, which can be detected by timeresolved fluorescence with short characteristic times. This is also reflected in FCS data by an increase in molecular brightness together with a decrease in the number of fluorescent molecules passing through the detection volume of the sample.
Exploring the pH-Induced Functional Phase Space of Human Serum Albumin by EPR Spectroscopy
Magnetochemistry
A systematic study on the self-assembled solution system of human serum albumin (HSA) and paramagnetic doxyl stearic acid (5-DSA and 16-DSA) ligands is reported covering the broad pH range 0.7–12.9, mainly using electron paramagnetic resonance (EPR) methods. It is tested to which extent the pH-induced conformational isomers of HSA reveal themselves in continuous wave (CW) EPR spectra from this spin probing approach in comparison to an established spin-labeling strategy utilizing 3-maleimido proxyl (5-MSL). Most analyses are conducted on empirical levels with robust strategies that allow for the detection of dynamic changes of ligand, as well as protein. Special emphasis has been placed on the EPR spectroscopic detection of a molten globule (MG) state of HSA that is typically found by the fluorescent probe 8-Anilino- naphthalene-1-sulfonic acid (ANS). Moreover, four-pulse double electron-electron resonance (DEER) experiments are conducted and substantiated with dynamic light scatteri...