Biophysical Chemistry Laboratory, Indian Institute of Chemical Biology, CSIR, Kolkata 700032, India.
Biophys Chem. 2011 Apr;155(1):10-9. doi: 10.1016/j.bpc.2011.01.011. Epub 2011 Feb 16.
The binding of two sugar containing antibiotics viz. aristololactam-β-D-glucoside and daunomycin with single and double stranded poly(A) was investigated by spectroscopic and calorimetric studies. The binding affinity of daunomycin to ss poly(A) was of the order of 10⁶ M⁻¹ and that to ds poly(A) was of the order of 10⁵ M⁻¹. Aristololactam-β-D-glucoside showed a relatively weaker binding with an affinity of the order of 10⁴ M⁻¹ with both the conformations of poly(A). Fluorescence studies showed maximum quenching for daunomycin-ss poly(A) complexes. The binding constants calculated from fluorescence spectroscopy were in good agreement with that obtained from UV spectroscopy. Moderate perturbation of circular dichroic spectra of both the conformations of poly(A) in presence of these molecules with concomitant formation of prominent extrinsic CD bands in the 300-450 nm region further revealed the association. Isothermal titration calorimetry results showed an overall entropy driven binding in all the four systems though the entropy change was maximum in daunomycin-ss poly(A) binding. The binding affinity was also maximum for daunomycin-ss poly(A) and varied as daunomycin-ds poly(A) > aristololactam-β-D-glucoside-ds poly(A) > aristololactam-β-D-glucoside-ss poly(A). A 1:1 binding stoichiometry was observed in all the cases, as confirmed by Job plot analysis, indicating the interaction to consist of a single binding mode. Ferrocyanide quenching studies showed good stacking interaction in all cases but was best for daunomycin-ss poly(A) interaction. No self-structure formation was observed in poly(A) with both daunomycin and aristololactam-β-D-glucoside suggesting the hindrance of the sugar moiety for such structural organization.
两种含糖抗生素（即阿利洛他汀-β-D-葡糖苷和柔红霉素）与单链和双链多聚（A）的结合通过光谱和量热研究进行了研究。柔红霉素与 ss 多聚（A）的结合亲和力约为 10⁶ M⁻¹，与 ds 多聚（A）的结合亲和力约为 10⁵ M⁻¹。阿利洛他汀-β-D-葡糖苷与两种构象的多聚（A）的结合相对较弱，亲和力约为 10⁴ M⁻¹。荧光研究表明，daunomycin-ss poly(A) 复合物的荧光猝灭程度最大。从荧光光谱计算得出的结合常数与从紫外光谱获得的结合常数非常吻合。这些分子存在时，两种构象的多聚（A）的圆二色性光谱均发生适度扰动，同时在 300-450nm 区域形成明显的外在圆二色性带，进一步证实了这种结合。等温滴定量热法结果表明，尽管在 daunomycin-ss poly(A) 结合中熵变最大，但在所有四个系统中均存在整体熵驱动的结合。结合亲和力在 daunomycin-ss poly(A) 结合中也是最大的，其变化规律为 daunomycin-ds poly(A) > aristololactam-β-D-glucoside-ds poly(A) > aristololactam-β-D-glucoside-ss poly(A)。通过 Job 作图分析确认了所有情况下均观察到 1:1 的结合化学计量比，表明该相互作用由单个结合模式组成。铁氰化物猝灭研究表明，所有情况下都存在良好的堆积相互作用，但 daunomycin-ss poly(A) 相互作用最佳。在 daunomycin 和阿利洛他汀-β-D-葡糖苷存在的情况下，多聚（A）均未观察到自结构形成，表明糖部分阻碍了这种结构组织。
