Department of Chemistry, American University of Beirut, Beirut, Lebanon.
Colloids Surf B Biointerfaces. 2012 Jun 1;94:354-61. doi: 10.1016/j.colsurfb.2012.02.017. Epub 2012 Feb 22.
Curcumin having pharmaceutical application as anti-oxidant, anti-inflammatory and anti-carcinogenic drug necessitates studying interaction of this molecule with native, unfolded and refolded state of human serum albumin (HSA), carrier protein in the blood. We proposed a simultaneous static and dynamic fluorescence quenching mechanism operating in the complex formation between HSA and curcumin. Location of curcumin in the close proximity of tryptophan with respect to tyrosine was further evident from the observation of two fold increase in rate of depletion of SFS intensity for tryptophan with respect to tyrosine in HSA in SFS spectrum. Alteration of SFS spectral peak position, electronic absorbance, fluorescence intensity and lifetime suggested chemical denaturation by urea expectedly unfold the protein molecule in the absence and presence of curcumin. Denatured HSA had similar fluorescence peak position and lifetime to that of L-tryptophan in the polar environment. During unfolding of HSA the spectral change of tyrosine and tryptophan was resolved through synchronous fluorescence spectra at two different Δλ in absence and presence of curcumin. It is found that curcumin remained bound to unfolded state of HSA and facilitated the process by pushing tryptophan moiety to more polar environment in the unfolded state. Dilution of the denatured protein by phosphate buffer reversibly refolded the sub-domain IIA, by also recovering fluorescence lifetime loss, but it was slow in the presence of curcumin. k(q) values indicate that curcumin-HSA complex is formed in the unfolded and refolded states as observed for native state.
姜黄素具有抗氧化、抗炎和抗癌药物的药用应用，因此需要研究该分子与血液中载体蛋白人血清白蛋白（HSA）的天然、展开和重折叠状态的相互作用。我们提出了一种同时的静态和动态荧光猝灭机制，该机制在 HSA 和姜黄素之间的复合物形成中起作用。姜黄素在色氨酸相对于酪氨酸的位置靠近，可以从观察到的 SFS 光谱中色氨酸相对于酪氨酸的 SFS 强度的消耗速率增加两倍进一步证明。SFS 光谱峰位置、电子吸收、荧光强度和寿命的改变表明，尿素的化学变性预计会在没有和存在姜黄素的情况下使蛋白质分子展开。变性的 HSA 在极性环境中具有与 L-色氨酸相似的荧光峰位置和寿命。在 HSA 的展开过程中，通过在 absence 和 presence 下的同步荧光光谱在两个不同的Δλ处解决了酪氨酸和色氨酸的光谱变化curcumin。结果发现，姜黄素仍然与 HSA 的展开状态结合，并通过将色氨酸部分推向展开状态的更极性环境来促进该过程。通过磷酸盐缓冲液稀释变性蛋白可使亚结构域 IIA 可逆地重新折叠，同时恢复荧光寿命的损失，但在 curcumin 存在时速度较慢。k(q) 值表明，如在天然状态下观察到的那样，姜黄素-HSA 复合物在展开和重折叠状态下形成。
