Joshi Ritika, Jadhao Manojkumar, Kumar Himank, Ghosh Sujit Kumar
Department of Chemistry, Visvesvaraya National Institute of Technology, Nagpur, Maharashtra 440010, India.
Department of Chemistry, Visvesvaraya National Institute of Technology, Nagpur, Maharashtra 440010, India.
Bioorg Chem. 2017 Dec;75:332-346. doi: 10.1016/j.bioorg.2017.10.013. Epub 2017 Nov 5.
A comparative biophysical study on the individual conformational adaptation embraced by two homologous serum albumins (SA) (bovine and human) towards a potential anticancer bioorganic compound 2-(6-chlorobenzo[d] thiazol-2-yl)-1H-benzo[de] isoquinoline-1,3(2H)- dione (CBIQD) is apparent from the discrimination in binding behavior and the ensuing consequences accomplished by combined in vitro optical spectroscopy, in silico molecular docking and molecular dynamics (MD) simulation. The Sudlow site I of HSA although anion receptive, harbors neutral CBIQD in Sudlow site I (subdomain IIA, close to Trp) of HSA, while in BSA its prefers to snugly fit into Sudlow site II (subdomain IIIA, close to Tyr). Based on discernable diminution of HSA mean fluorescence lifetime as a function of biluminophore concentration, facile occurrence of fluorescence resonance energy transfer (FRET) is substantiated as the probable quenching mechanism accompanied by structural deformations in the protein ensemble. CBIQD establishes itself within HSA close to Trp214, and consequently reduces the micropolarity of the cybotactic environment that is predominantly constituted by hydrophobic amino acid residues. The stronger association of CBIQD with HSA encourages an allosteric modulation leading to slight deformation in its secondary structure whereas for BSA the association is comparatively weaker. Sudlow site I of HSA is capable to embrace a favorable conformation like malleable gold to provide room for incoming CBIQD, whereas for BSA it behaves more like rigid cast-iron which does not admit any change thus forcing CBIQD to occupy an altogether different binding location i.e. the Sudlow site II. The anticancer CBIQD is found to be stable within the HSA scaffold as vindicated by root mean square deviation (RMSD) and root mean square fluctuation (RMSF) obtained by MD simulation. A competitively inhibited esterase-like activity of HSA upon CBIQD binding to Lys199 and Arg257 residues, plausibly envisions that similar naphthalimide based prodrugs, bearing ester functionality, can be particularly activated by Sudlow site I of HSA. The consolidated spectroscopic research described herein may encourage design of naphthalimide based pro-drugs for effective in vivo biodistribution using HSA-based drug delivery systems.
通过体外光谱学、计算机辅助分子对接和分子动力学（MD）模拟相结合，对两种同源血清白蛋白（SA）（牛血清白蛋白和人血清白蛋白）对潜在抗癌生物有机化合物2-(6-氯苯并[d]噻唑-2-基)-1H-苯并[de]异喹啉-1,3(2H)-二酮（CBIQD）的个体构象适应性进行了比较生物物理研究。从结合行为的差异以及由此产生的结果可以明显看出，人血清白蛋白（HSA）的Sudlow位点I虽然具有阴离子接受能力，但在HSA的Sudlow位点I（亚结构域IIA，靠近色氨酸）中容纳中性的CBIQD，而在牛血清白蛋白（BSA）中，它更倾向于紧密地结合在Sudlow位点II（亚结构域IIIA，靠近酪氨酸）中。基于HSA平均荧光寿命随双荧光团浓度的明显降低，证实了荧光共振能量转移（FRET）的容易发生是可能的猝灭机制，同时伴随着蛋白质整体结构的变形。CBIQD在HSA中靠近Trp214的位置确定下来，从而降低了主要由疏水氨基酸残基构成的近程环境的微极性。CBIQD与HSA的更强结合促进了变构调节，导致其二级结构发生轻微变形，而对于BSA，这种结合相对较弱。HSA的Sudlow位点I能够像可锻金一样呈现出有利的构象，为进入的CBIQD提供空间，而对于BSA，它的行为更像刚性铸铁，不允许任何变化，从而迫使CBIQD占据完全不同的结合位置，即Sudlow位点II。MD模拟得到的均方根偏差（RMSD）和均方根波动（RMSF）表明，抗癌CBIQD在HSA支架内是稳定的。CBIQD与HSA的Lys199和Arg257残基结合后，HSA的酯酶样活性受到竞争性抑制，这合理地设想，类似的带有酯功能的萘酰亚胺类前药可以被HSA的Sudlow位点I特别激活。本文所述的综合光谱研究可能会鼓励设计基于萘酰亚胺的前药，以利用基于HSA的药物递送系统实现有效的体内生物分布。
