Raut Sangram, Chib Rahul, Butler Susan, Borejdo Julian, Gryczynski Zygmunt, Gryczynski Ignacy
Center for Fluorescence Technologies and Nanomedicine, Department of Cell Biology and immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
Department of Physics. Texas Christian University, 2800 S. University Dr., Fort Worth, Texas, USA, 76129.
Methods Appl Fluoresc. 2014 Sep;2(3). doi: 10.1088/2050-6120/2/3/035004. Epub 2014 Aug 20.
This work reports on the chromophores interactions within protein-protected gold nanoclusters. We conducted spectroscopic studies of fluorescence emissions originated from gold nanoclusters and intrinsic tryptophan (Trp) in BSA or HSA proteins. Both, steady state fluorescence and lifetime measurements show a significant Forster resonance energy transfer (FRET) from Trp to the gold nanocluster. Tryptophan lifetimes in the case of protein-protected gold nanoclusters are 2.6ns and 2.3ns for BSA and HSA Au clusters while 5.8ns for native BSA and 5.6 for native HSA. The apparent distances from Trp to gold nanocluster emission center, we estimated as 24.75A for BSA and 23.80A for HSA. We also studied a potassium iodide (KI) quenching of protein-protected gold nanoclusters and compared with the quenching of BSA and HAS alone. The rates of Trp quenching were smaller in BSA-Au and HSA-Au nanoclusters than in the case of free proteins, which is consistent with shorter lifetime of quenched Trp(s) and lower accessibility for KI. While Trp residues were quenched by KI, the emissions originated from nanoclusters were practically unquenched. In summary, for BSA and HSA Au clusters, we found 55% and 59% energy transfer efficiency respectively from tryoptophan to gold clusters. We believe this interaction can be used to our advantage in terms of developing resonance energy transfer based sensing applications.
这项工作报道了蛋白质保护的金纳米团簇内发色团之间的相互作用。我们对源自金纳米团簇以及牛血清白蛋白（BSA）或人血清白蛋白（HSA）蛋白质中固有色氨酸（Trp）的荧光发射进行了光谱研究。稳态荧光和寿命测量均表明存在从Trp到金纳米团簇的显著福斯特共振能量转移（FRET）。对于蛋白质保护的金纳米团簇，BSA和HSA金团簇中色氨酸的寿命分别为2.6纳秒和2.3纳秒，而天然BSA中为5.8纳秒，天然HSA中为5.6纳秒。我们估计从Trp到金纳米团簇发射中心的表观距离，对于BSA为24.75埃，对于HSA为23.80埃。我们还研究了碘化钾（KI）对蛋白质保护的金纳米团簇的猝灭作用，并与单独的BSA和HSA的猝灭情况进行了比较。在BSA-Au和HSA-Au纳米团簇中，Trp的猝灭速率比游离蛋白质的情况要小，这与猝灭的Trp寿命较短以及KI的可及性较低是一致的。当Trp残基被KI猝灭时，源自纳米团簇的发射实际上未被猝灭。总之，对于BSA和HSA金团簇，我们分别发现从色氨酸到金团簇的能量转移效率为55%和59%。我们相信这种相互作用在开发基于共振能量转移的传感应用方面对我们有利。
