Department of Chemistry, West Bengal State University, Barasat, Kol-126, India.
Department of Microbiology, West Bengal State University, Barasat, Kol-126, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2017 Mar 15;175:191-199. doi: 10.1016/j.saa.2016.12.032. Epub 2016 Dec 21.
An environment sensitive fluorophore, 4-(5-(4-(dimethylamino)phenyl)oxazol-2-yl)benzoic acid (DMOBA), that closely mimics biologically active 2,5-disubstituited oxazoles has been designed to probe two homologous serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA) by means of photophysical and molecular modeling studies. This fluorescent analogue exhibits solvent polarity sensitive fluorescence due to an intramolecular charge transfer in the excited state. In comparison to water, the steady state emission spectra of DMOBA in BSA is characterized by a greater blue shift (10nm) and smaller Stokes' shift (5980cm) in BSA than HSA (Stokes'shift6600cm), indicating less polar and more hydrophobic environment of the dye in the former than the latter. The dye-protein binding interactions are remarkably stronger for BSA than HSA which is evident from higher value of the association constant for the DMOBA-BSA complex (K5.2×10M) than the DMOBA-HSA complex (K~1.0×10M). Fӧrster resonance energy transfer studies revealed remarkably less efficient energy transfer (8%) between the donor tryptophans in BSA and the acceptor DMOBA dye than that (30%) between the single tryptophan moiety in HSA and the dye, which is consistent with a much larger distance between the donor (tryptophan)-acceptor (dye) pair in BSA (34.5Å) than HSA (25.4Å). Site specific competitive binding assays have confirmed on the location of the dye in Sudlow's site II of BSA and in Sudlow's site I of HSA, respectively. Molecular modeling studies have shown that the fluorescent analogue is tightly packed in the binding site of BSA due to strong steric complementarity, where, binding of DMOBA to BSA is primarily dictated by the van der Waals and hydrogen bonding interactions. In contrast, in HSA the steric complementarity is less significant and binding is primarily guided by polar interactions and van der Waals interactions appear to be less significant in the formation of the HSA-DMOBA complex. Electrostatic interactions contribute significantly in the binding of DMOBA to HSA (-2.09kcal/mol) compared to BSA (-0.47kcal/mol). Electrostatic surface potential calculation reveals that the DMOBA binding site within HSA is highly charged compared to BSA.
一种环境敏感的荧光团，4-(5-(4-(二甲基氨基)苯基)恶唑-2-基)苯甲酸(DMOBA)，通过光物理和分子建模研究，设计用来探测两种同源血清蛋白，人血清白蛋白(HSA)和牛血清白蛋白(BSA)。与水相比，DMOBA 在 BSA 中的稳态发射光谱的蓝移更大(10nm)，Stokes 位移更小(5980cm)，表明在前者中染料的极性更小，疏水性环境比后者更大。与 HSA 相比，DMOBA 与 BSA 的结合相互作用要强得多，这从 DMOBA-BSA 复合物的结合常数(K5.2×10M)比 DMOBA-HSA 复合物(K1.0×10M)高就可以明显看出。Fӧrster 共振能量转移研究表明，与 HSA 中单个色氨酸部分和染料之间的能量转移效率(30%)相比，BSA 中供体色氨酸和受体 DMOBA 染料之间的能量转移效率显著降低(8%)，这与 BSA 中供体(色氨酸)-受体(染料)对之间的距离明显大于 HSA 中(25.4Å)的距离(34.5Å)一致。位点特异性竞争结合实验分别证实了 DMOBA 在 BSA 的 Sudlow 位点 II 和 HSA 的 Sudlow 位点 I 中的位置。分子建模研究表明，由于强立体互补性，荧光类似物在 BSA 的结合部位紧密堆积，其中 DMOBA 与 BSA 的结合主要由范德华力和氢键相互作用决定。相比之下，在 HSA 中，立体互补性不那么显著，结合主要由极性相互作用指导，范德华相互作用在 HSA-DMOBA 复合物的形成中似乎不那么重要。与 BSA(-0.47kcal/mol)相比，静电相互作用在 DMOBA 与 HSA 的结合中显著贡献(-2.09kcal/mol)。静电表面电势计算表明，与 BSA 相比，HSA 中 DMOBA 的结合位点带电荷量更高。
