The aim of present study was to investigate the binding interactions of a model hydrophobic molecule, dimethylcurcumin (DMC) with nanoparticle form of bovine serum albumin (BSA) using fluorescence spectroscopy techniques. For this, BSA nanoparticles (size = 62.0 ± 3.5 nm, molecular weight = 11,243 ± 3445 kD) prepared by thermal denaturation method was mixed with DMC in solution and monitored for fluorescence emission of tryptophan (Trp) residue as well as DMC separately. The emission maximum of DMC in nanoparticles form exhibited more blue sift and quenched the excited state of tryptophan (Trp) by six fold higher than in the native form of BSA. By analyzing Trp fluorescence, the mean binding constant (K) estimated for the interaction of DMC with native and nanoparticles forms of BSA was 2.7 ± 0.4 × 10⁴ M⁻¹ and 1.5 ± 0.5 × 10⁵ M⁻¹ respectively. Together these results suggested that DMC experienced a more rigid environment in nanoparticles than in native form of BSA. Additionally the above determined K values were in agreement with those reported previously by absorption techniques. Further direct energy transfer was observed between Trp and DMC, using which the distance (r) calculated between them was 28.25 ± 0.27 Ǻ in BSA native. Similar analysis involving BSA nanoparticle and DMC revealed a distance of 24.25 ± 1.05 Ǻ between the hydrophobic core and the ligand. Finally interaction of DMC with BSA was validated through molecular docking studies, which indicated sub-domain IIA as the binding site of DMC. Thus it is concluded that intrinsic fluorescence of protein can be utilized to study the interaction of its different physical forms with any hydrophobic ligand.

中文翻译：

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模型疏水性药物二甲基姜黄素与白蛋白纳米颗粒的相互作用。

本研究的目的是使用荧光光谱技术研究模型疏水分子二甲基姜黄素（DMC）与牛血清白蛋白（BSA）的纳米颗粒形式的结合相互作用。为此，将通过热变性法制备的BSA纳米颗粒（尺寸= 62.0±3.5 nm，分子量= 11,243±3445 kD）与DMC混合，并分别监测色氨酸（Trp）残留物和DMC的荧光发射。纳米颗粒形式的DMC的最大发射展示出更多的蓝色筛分，并且使色氨酸（Trp）的激发态比BSA的天然形式高出六倍。通过分析Trp荧光，估计DMC与天然和纳米颗粒形式的BSA相互作用的平均结合常数（K）为2.7±0.4×10 ⁴  M^-1和1.5±0.5×10 ⁵  M ^-1分别。这些结果共同表明，DMC在纳米颗粒中比在天然形式的BSA中经历了更严格的环境。另外，上述确定的K值与先前通过吸收技术报道的那些值一致。在Trp和DMC之间观察到了进一步的直接能量转移，在BSA本机中，它们之间的距离（r）计算为28.25±0.27Ǻ。涉及BSA纳米颗粒和DMC的类似分析显示，疏水核和配体之间的距离为24.25±1.05Ǻ。最后，通过分子对接研究验证了DMC与BSA的相互作用，表明亚域IIA是DMC的结合位点。因此得出结论，可以利用蛋白质的固有荧光来研究其不同物理形式与任何疏水性配体的相互作用。