BackgroundInteraction of aristololactam-β-D-glucoside and daunomycin with tRNAphe was investigated using various biophysical techniques.Methodology/Principal FindingsAbsorption and fluorescence studies revealed that both the compounds bind tRNAphe non-cooperatively. The binding of daunomycin was about one order of magnitude higher than that of aristololactam-β-D-glucoside. Stronger binding of the former was also inferred from fluorescence quenching data, quantum efficiency values and circular dichroic results. Results from isothermal titration calorimetry experiments suggested that the binding of both compounds was predominantly entropy driven with a smaller but favorable enthalpy term that increased with temperature. A large favorable electrostatic contribution to the binding of daunomycin to tRNAphe was revealed from salt dependence data and the dissection of the free energy values. The electrostatic component to the free energy change for aristololactam-β-D-glucoside-tRNAphe interaction was smaller than that of daunomycin. This was also inferred from the slope of log K versus [Na+] plots. Both compounds enhanced the thermal stability of tRNAphe. The small heat capacity changes of -47 and -99 cal/mol K, respectively, observed for aristololactam-β-D-glucoside and daunomycin, and the observed enthalpy-entropy compensation phenomenon confirmed the involvement of multiple weak noncovalent interactions. Molecular aspects of the interaction have been revealed.Conclusions/SignificanceThis study presents the structural and eneregetic aspects of the binding of aristololactam-β-D-glucoside and daunomycin to tRNAphe.
Background & AimsIncreasing age is associated with impaired immune function and in chronic HCV infection specifically, with progressive fibrosis, liver failure, HCC and impaired responses to antiviral therapy. T-lymphocyte telomere length declines with age. We hypothesised that shorter T-lymphocyte telomere length would be associated with poor clinical outcome in HCV infection.MethodsCirculating T-lymphocyte telomere length, an objective measure of immune senescence, was measured by flow-FISH in 135 HCV-RNA-positive, treatment-naïve patients and 41 healthy controls in relation to clinical outcome.ResultsShorter CD4+CD45RO+ T-lymphocyte telomeres were associated with severe fibrosis (p = 0.003), independent of male sex (p = 0.04), CMV positivity (p = 0.003), previous HBV infection (p = 0.007), and age (p = ns) in viraemic patients compared to controls. There were inverse correlations between CD4+CD45RO+ telomere length and fibrosis stage (p <0.001), portal tract inflammatory grade (p = 0.035), prothrombin time (p <0.001) and bilirubin (p = 0.001). One hundred and twenty-four viraemic individuals were followed prospectively to a composite endpoint of death, hepatic decompensation or HCC. Independent of age, those with shorter CD4+CD45RO+ telomeres were less likely to be complication free after 2-years than those with longer telomeres (86% versus 96%, p = 0.009) with an age-adjusted hazard ratio of 0.93 (0.90–0.96). In addition, CD4+CD45RO+ telomere length predicted successful antiviral therapy (p = 0.001) independent of other factors.ConclusionsCD4+ T-lymphocyte telomere length, independent of age, was related to inflammatory grade, fibrosis stage, laboratory indices of severity, subsequent hepatic decompensation and treatment outcome in patients with chronic HCV infection.
The plant alkaloid aristololactam-β-d-glucoside and the anticancer chemotherapy drug daunomycin are two sugar bearing DNA binding antibiotics. The binding of these molecules to three double stranded ribonucleic acids, poly(A)·poly(U), poly(I)·poly(C) and poly(C)·poly(G), was studied using various biophysical techniques. Absorbance and fluorescence studies revealed that these molecules bound non-cooperatively to these ds RNAs with the binding affinities of the order 10(6) for daunomycin and 10(5) M(-1) for aristololactam-β-d-glucoside. Fluorescence quenching and viscosity studies gave evidence for intercalative binding. The binding enhanced the melting temperature of poly(A)·poly(U) and poly(I)·poly(C) and the binding affinity values evaluated from the melting data were in agreement with that obtained from other techniques. Circular dichroism results suggested minor conformational perturbations of the RNA structures. The binding was characterized by negative enthalpy and positive entropy changes and the affinity constants derived from calorimetry were in agreement with that obtained from spectroscopic data. Daunomycin bound all the three RNAs stronger than aristololactam-β-d-glucoside and the binding affinity varied as poly(A)·poly(U) > poly(I)·poly(C) > poly(C)·poly(G). The temperature dependence of the enthalpy changes yielded negative values of heat capacity changes for the complexation suggesting substantial hydrophobic contribution to the binding process. Furthermore, an enthalpy-entropy compensation behavior was also seen in all systems. These results provide new insights into binding of these small molecule drugs to double stranded RNA sequences.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.