ABSTRACT
Surface-enhanced Raman spectroscopy was employed in this work to study the interaction between the antitumoral drug emodin and human serum albumin (HSA), as well as the influence of fatty acids in this interaction. We demonstrated that the drug/protein interaction can take place through two different binding sites which are probably localized in the IIA and IIIA hydrophobic pockets of HSA and which correspond to Sudlow's I and II binding sites, respectively. The primary interaction site of this drug seems to be site II in the defatted albumin. Fatty acids seem to displace the drug from site II to site I in nondefatted HSA, due to the high affinity of fatty acids for site II. The drug interacts with the protein through its dianionic form in defatted HSA (when placed in the site II) and through its neutral form in the site I of nondefatted albumins.
Subject(s)
Antineoplastic Agents/pharmacology , Emodin/pharmacology , Enzyme Inhibitors/pharmacology , Serum Albumin/pharmacology , Spectrum Analysis, Raman/methods , Binding Sites , Fatty Acids/chemistry , Humans , Hydrogen Bonding , Hydrogen-Ion Concentration , Ligands , Models, Chemical , Protein Binding , Ultraviolet RaysABSTRACT
Surface-enhanced Raman spectroscopy, resonance Raman spectroscopy and molecular modeling were employed to study the interaction of hypericin (Hyp) with human (HSA), rat (RSA) and bovine (BSA) serum albumins. The identification of the binding site of Hyp in serum albumins as well as the structural model for Hyp/HSA complex are presented. The interactions mainly reflect: (1) a change of the strength of H bonding at the N1-H site of Trp; (2) a change of the Trp side-chain conformation; (3) a change of the hydrophobicity of the Trp environment; and (4) a formation of an H-bond between the carbonyl group of Hyp and a proton donor in HSA and RSA which leads to a protonated-like carbonyl in Hyp. Our results indicate that Hyp is rigidly bound in IIA subdomain of HSA close to Trp214 (distance 5.12 A between the centers of masses). In the model presented the carbonyl group of Hyp is hydrogen bonded to Asn458. Two other candidates for hydrogen bonds have been identified between the bay-region hydroxyl group of Hyp and the carbonyl group of the Trp214 peptidic link and between the peri-region hydroxyl group of Hyp and the Asn458 carbonyl group. It is shown that the structures of the Hyp/HSA and Hyp/RSA complexes are similar to, and in some aspects different from, those found for the Hyp/BSA complex. The role of aminoacid sequence in the IIA subdomains of HSA, RSA and BSA is discussed to explain the observed differences.
Subject(s)
Perylene/analogs & derivatives , Perylene/chemistry , Perylene/pharmacokinetics , Photosensitizing Agents/chemistry , Photosensitizing Agents/pharmacokinetics , Serum Albumin/chemistry , Serum Albumin/metabolism , Animals , Anthracenes , Cattle , Humans , Hydrogen Bonding , In Vitro Techniques , Models, Molecular , Molecular Conformation , Photochemistry , Rats , Spectrum Analysis, RamanABSTRACT
Poly(dI-dC) in H2O and D2O solution can undergo different equilibrium geometries which strongly depend on the salt nature and concentration. These structures were studied by classical Raman spectroscopy in order to monitor a hydrogen-deuterium exchange kinetics in 8-CH group in inosine. Spectral and isotopic exchange rate changes depending on NaCl concentration were observed and interpreted on the basis of previously obtained results from resonance and classical Raman spectroscopy studies of poly(dI-dC) and hydrogen-deuterium exchange measurements of different conformations of nucleic acids. It is shown that: i) the Raman spectrum of low-salt poly(dI-dC) corresponds to the right-handed polymer with characteristic bands for B conformation, but the value of the retardation factor of isotopic exchange suggests that this form is not a pure canonical B form and that it contains some portion of the A form, ii) the Raman spectrum of the high-salt poly(dI-dC) corresponds to the right-handed polymer with characteristic bands for both the A and B conformations, iii) the retardation factor of hydrogen deuterium exchange for the high-salt form of poly(dI-dC) is essentially higher than in the low-salt form which indicates a dominant presence of the A form in the high-salt conformation of poly(dI-dC). This leads to the conclusion that the high-salt conformation of poly(dI-dC) is a mixture of A and B forms with the predominant A form.
Subject(s)
Nucleic Acid Conformation , Polydeoxyribonucleotides/chemistry , Spectrum Analysis, Raman , Deuterium , Hydrogen , Kinetics , Sodium Chloride , Spectrum Analysis, Raman/methodsABSTRACT
Poly(dI-dC) in aqueous solution can undergo different equilibrium geometries which strongly depend on the salt nature and the concentration. These structures were studied by classical Raman spectroscopy (RS). Spectral changes depending on NaCl concentration and on the presence of Ni2+ ions were observed and interpreted on the basis of previously obtained results from resonance RS studies of poly(dI-dC) and classical RS studies for other alternating purine-pyrimidine polydeoxyribonucleotides, i.e. poly(dG-dC), poly(dA-dT) and poly(dA-dC)(dG-dT), which also showed B to Z conformational transitions upon varying the salt concentrations. It is shown that: i) The low-salt structure (0.1 mol/l NaCl) is in the pure canonical B conformation. ii) The high-salt (5 mol/l NaCl) Raman spectrum is similar to that obtained for the low-salt concentration. Thus the high-salt structure corresponds to the right-handed polymer with characteristic bands for both the B (predominant) and A conformations with some weak Z conformation markers which indicate a tendency for B to Z conformational transition of the polymer. iii) The addition of 9.10(-3) mol/l NiCl2 to the high-salt solution induces Z-conformation of the polymer.
