Interaction of the Anticancer Plant Alkaloid Sanguinarine with Bovine Serum Albumin

Background: Interaction of the iminium and alkanolamine forms of sanguinarine with bovine serum albumin (BSA) was characterized by spectroscopic and calorimetric techniques. Methodology/Principal Findings: Formation of strong complexes of BSA with both iminium and alkanolamine forms was revealed from fluorescence quenching of sanguinarine. Binding parameters calculated from Stern-Volmer quenching method revealed that the neutral alkanolamine had higher affinity to BSA compared to the charged iminium form. Specific binding distances of 3.37 and 2.38 nm between Trp 212 (donor) and iminium and alkanolamine forms (acceptor), respectively, were obtained from Forster resonance energy transfer studies. Competitive binding using the site markers warfarin and ibuprofen, having definite binding sites, demonstrated that both forms of sanguinarine bind to site I (subdomain IIA) on BSA. Sanguinarine binding alters protein conformation by reducing the a-helical organization and increasing the coiled structure, indicating a small but definitive partial unfolding of the protein. Thermodynamic parameters evaluated from isothermal titration calorimetry suggested that the binding was enthalpy driven for the iminium form but favoured by negative enthalpy and strong favourable entropy contributions for the alkanolamine form, revealing the involvement of different molecular forces in the complexation. Conclusions/Significance: The results suggest that the neutral alkanolamine form binds to the protein more favourabl

Biophysical Characterization of the Strong Stabilization of the RNA Triplex poly(U)•poly(A)*poly(U) by 9-O-(ω-amino) Alkyl Ether Berberine Analogs

Background: Binding of two 9-O-(v-amino) alkyl ether berberine analogs BC1 and BC2 to the RNA triplex poly(U)Npoly(A)*poly(U) was studied by various biophysical techniques. Methodology/Principal Findings: Berberine analogs bind to the RNA triplex non-cooperatively. The affinity of binding was remarkably high by about 5 and 15 times, respectively, for BC1 and BC2 compared to berberine. The site size for the binding was around 4.3 for all. Based on ferrocyanide quenching, fluorescence polarization, quantum yield values and viscosity results a strong intercalative binding of BC1 and BC2 to the RNA triplex has been demonstrated. BC1 and BC2 stabilized the Hoogsteen base paired third strand by about 18.1 and 20.5uC compared to a 17.5uC stabilization by berberine. The binding was entropy driven compared to the enthalpy driven binding of berbeine, most likely due to additional contacts within the grooves of the triplex and disruption of the water structure by the alkyl side chain. Conclusions/Significance: Remarkably higher binding affinity and stabilization effect of the RNA triplex by the amino alkyl berberine analogs was achieved compared to berberine. The length of the alkyl side chain influence in the triplex stabilization phenomena

Biophysical studies on the interaction of some intercalating and groove binding molecules with deoxyribonucleic acids

The mode of action of many drugs in clinical use for the treatment of cancer, genetic disorders and viral diseases is essentially based on their binding to DNA and the subsequent modifications of the genetic material (Hurley et al., 1996; Rezler et al., 2003; Hurley, 2001 and 2002). Therefore, interest in understanding the interaction of small molecule ligands with DNA sequences has been the subject of intense investigations for almost half a century (Waring, 1981) (Chaires, 1998) (Maiti and Kumar, 2007). Despite a large number of DNA binding drugs currently in use in clinics for cancer treatment, selectivity towards malignant cells remains an elusive goal. More detailed knowledge and deeper insights of the DNA interaction ....

Thermodynamic Profiles of The DNA Binding of Benzophenanthridines Sanguinarine and Ethidium: A Comparative Study with Sequence Specific Polynucleotides

Energetics of the binding of two known classical DNA intercalating molecules, ethidium and sanguinarine with four sequence specific polynucleotides, poly(dG-dC).poly(dG-dC), poly(dG).poly(dC), poly(dAdT). poly(dA-dT), and poly(dA).poly(dT) have been compared under identical conditions. The binding of both the molecules was characterized by strong stabilization of the polynucleotides against thermal strand separation in optical melting as well as differential scanning calorimetry studies. Isothermal titration calorimetry results revealed that the binding of both sanguinarine and ethidium to poly(dG-dC).poly( dG-dC), poly(dA-dT).poly(dA-dT), and poly(dG).poly(dC) was exothermic and favoured by negative enthalpy changes. On the other hand, the binding of both molecules to poly(dA).poly(dT) was endothermic and entropy driven. The binding affinity values obtained from isothermal titration calorimetry data was in close proximity to that derived from thermal melting data. The heat capacity changes obtained from temperature dependence of the enthalpy change gave negative values in the range (�0.4 to 1.25) kJ � mol�1 � K�1 for the binding of ethidium and sanguinarine to these polynucleotides. The variations in the values indicate important differences in the formation of the complexes. New insights into the energetics and specificity aspects of interaction of these molecules to DNA have emerged from these studies

RNA Specific Molecules: Cytotoxic Plant Alkaloid Palmatine Binds Strongly to Poly(A)

Abstract—The cytotoxic plant alkaloid palmatine was found to bind strongly by partial intercalation to single stranded poly(A) structure with binding affinity (Ka) of (8.36 ± 0.26) · 105 M�1. The binding of palmatine was characterized to be exothermic and enthalpy driven with one palmatine for every two adenine residues. On the other hand, the binding to the double stranded poly(A) has been found to be significantly weak. This study identifies poly(A) as a potential bio-target for the alkaloid palmatine and its use as a lead compound in antitumor drug screening

DNA Intercalation by Quinacrine and Methylene Blue: A Comparative Binding and Thermodynamic Characterization Study

There is compelling evidence that cellular DNA is the target of many anticancer agents. Consequently, elucidation of the molecular nature governing the interaction of small molecules to DNA is paramount to the progression of rational drug design strategies. In this study, we have compared the binding and thermodynamic aspects of two known DNA-binding agents, quinacrine (QNA) and methylene blue (MB), with calf thymus (CT) DNA. The study revealed noncooperative binding phenomena for both the drugs to DNA with an affinity one order higher for QNA compared to MB as observed from diverse techniques, but both bindings obeyed neighbor exclusion principle. The data of the salt dependence of QNA and MB fromthe plot of log K versus log [Na+] revealed a slope of 1.06 and 0.93 consistent with the values predicted by theories for the binding of monovalent cations, and have been analyzed for contributions from polyelectrolytic and nonpolyelectrolytic forces. The binding of both drugs was further characterized by strong stabilization of DNA against thermal strand separation in both optical melting and differential scanning calorimetry studies. The binding data analyzed from the thermal denaturation and from isothermal titration calorimetry (ITC) were in close proximity to those obtained from spectral titration data. ITC results revealed the binding to be exothermic and favored by both negative enthalpy and positive entropy changes. The heat capacity changes obtained from temperature dependence of enthalpy indicated�146 and�78 cal=(mol�K), respectively, for the binding of QNA and MB to CT DNA. Circular dichroism study further characterized the structural changes on DNA upon intercalation of these molecules. Molecular aspects of interaction of these molecules to DNA are discussed

Interaction of Small Molecules with Double-Stranded RNA: Spectroscopic, Viscometric, and Calorimetric Study of Hoechst and Proflavine Binding to PolyCG Structures

Design and synthesis of new small molecules binding to double-stranded RNA necessitate complete understanding of the molecular aspects of the binding of many existing molecules. Toward this goal, in this work we evaluated the biophysical aspects of the interaction of a DNA intercalator (proflavine) and a minor groove binder (hoechst 33258) with two polymorphic forms of polyCG, namely, the right-handed Watson-Crick base paired A-form and the left-handed Hoogsteen base paired HL-form, by absorption, fluorescence, and viscometry experiments. The energetics of the interaction of these molecules with the RNA structures has also been elucidated by isothermal titration calorimetry (ITC). Results suggest that proflavine strongly intercalates in both forms of polyCG, whereas hoechst shows mainly groove-binding modes. The binding of both drugs to both forms of RNA resulted in significant conformational change to the RNA structure with the bound molecules being placed in the chiral RNA helix. ITC profiles for both proflavine and hoechst show two binding sites. Binding of proflavine to both forms of RNA is endothermic and entropy driven in the first site and exothermic and enthalpy driven in the second site, whereas hoechst binding to both forms of RNA is exothermic and enthalpy driven in the first site and endothermic and entropy driven in the second site. This study suggests that the binding affinity characteristics and energetics of interaction of these DNA binding molecules with the RNA conformations are significantly different and may serve as data for future development of effective structureselective RNA-based drugs

Performance Analysis of a High Voltage DC (HVDC) Transmission System under Steady State and Faulted Conditions

The modern High Voltage Direct Current (HVDC) transmission technology depends on the development of power electronics based on the semiconductor devices. This paper represents a simple model of HVDC transmission system in which the converter and filter have been designed to increase stability of power transmission. The HVDC transmission system has been proposed on the basis of simulation studies using MATLAB software package (Simulink Model). Using this model, current - voltage (C-V) characteristics have been simulated for steady state condition. It has also been studied for different fault conditions.  With the proposed strategy the HVDC system can provide useful and economical way to transmit electric power over the long distance, thereby improving the bulk transmission of electric power and power system stability

Binding of Plant Alkaloids Berberine and Palmatine to Serum Albumins: A Thermodynamic Investigation

The thermodynamics of the interaction of two pharmaceutically important isoquinoline alkaloids berberine and palmatine with bovine and human serum albumin was investigated using calorimetric techniques, and the data was supplemented with fluorescence and circular dichroism studies. Thermodynamic results revealed that there was only one class of binding sites for both alkaloids on BSA and HSA. The equilibrium constant was of the order of 104 M-1 for both the alkaloids to serum albumins but the magnitude was slightly higher with HSA. Berberine showed higher affinity over palmatine to both proteins. The binding was enthalpy dominated and entropy favoured for both the alkaloids to BSA and HSA. Salt dependent studies suggested that electrostatic interaction had a significant role in the binding process, the binding affinity reduced as the salt concentration increased. Temperature dependent calorimetric data yielded heat capacity values that suggested the involvement of different molecular forces in the complexation of the two alkaloids with BSA and HSA. 3D fluorescence, synchronous fluorescence and circular dichroism data suggested that the binding of the alkaloids changed the conformation of proteins by reducing their helicity. Destabilization of the protein conformation was also revealed from differential scanning calorimetry studies. Overall, the alkaloids bound strongly to serum albumins, but berberine was a better binder to both serum proteins compared to palmatin

Enhanced DNA Binding of 9-o-Amino Alkyl Ether Analogs from the Plant Alkaloid Berberine

To understand the structure–activity relationship of isoquinoline alkaloids, absorption, fluorescence, circular dichroism, and thermodynamics were employed to study the interaction of five C-9-o-amino alkyl ether analogs from the plant alkaloid berberine with double-stranded calf thymus DNA. The C-9 derivatization resulted in dramatic enhancements in the fluorescence emission of these compounds. The most remarkable changes in the spectral and binding properties were in the BC4 and BC5 derivatives. Interactions of these analogs, which have an additional recognition motif with DNA, were evaluated through different spectroscopic and calorimetric titration experiments. The analogs remarkably enhanced the DNA binding affinity and the same was directly dependent on the alkyl chain length. The analog with six alkyl chains enhanced the DNA binding affinity by about 33 times compared with berberine. The binding became more entropically driven with increasing chain length. These results may be of potential use in the design of berberine derivatives and understanding of the structure–activity relationship for improved therapeutic applications