Design and Synthesis of Fluorescent Probe for Polyhistidine Tag Using Macrocyclic Nickel(II) Complex and Fluorescein Conjugate
作者:Masayasu Taki、Fumiyoshi Asahi、Tasuku Hirayama、Yukio Yamamoto
DOI:10.1246/bcsj.20100288
日期:2011.4.15
We report a newly designed polyhistidine tag (His-tag) targeting fluorescent probe, NiLODCF, which we synthesized based on the fluorophore displacement mechanism. A macrocyclic nickel(II) complex (NiLO) was employed as a novel binding site for a His-tag motif, and we chose dichlorofluorescein (DCF) (=2′,7′-dichloro-3′,6′-dihydroxyspiro[isobenzofuran-1(3H),9′-(9H)xanthen]-3-one) as the fluorophore. A hypochromic shift of NiLODCF from the metal-unbound form (LODCF) in the absorption spectrum suggested that the phenolic oxygen atom of DCF interacted directly with the NiLO complex, resulting in efficient fluorescence quenching (Φ = 0.084) in a neutral aqueous solution. When a model peptide having a hexahistidine sequence (H6Y1: YHHHHHH) was added to the solution of NiLODCF, a significant fluorescence enhancement in the emission (Φ = 0.60) was observed. The stoichiometry of the ternary complex between NiLODCF and H6Y1 was 1:1. The fluorescence intensity increased as the concentration of H6Y1 increased, and the dissociation constant (Kd) was determined to be 24 ± 1 µM, consistent with that for the Ni–NTA complex and His6-fused proteins (Kd = 1–20 µM). These results indicate that macrocyclic NiLO can serve as a novel binding site for the polyhistidine sequence and that NiLODCF would be applicable to a switchable fluorescent probe for such His-tagged proteins.
我们报告了一种新设计的聚组氨酸标签(His-tag)靶向荧光探针--NiLODCF,该探针是我们基于荧光团置换机制合成的。我们利用大环镍(II)配合物(NiLO)作为 His-tag 主题的新型结合位点,并选择二氯荧光素(DCF)(=2′,7′-二氯-3′,6′-二羟基螺[异苯并呋喃-1(3H),9′-(9H)氧杂蒽]-3-酮)作为荧光团。在吸收光谱中,NiLODCF 与金属未结合形式(LODCF)相比发生了低色度偏移,这表明 DCF 的酚氧原子直接与 NiLO 复合物相互作用,从而在中性水溶液中产生了有效的荧光淬灭(Φ = 0.084)。当在 NiLODCF 溶液中加入具有六组氨酸序列(H6Y1: YHHHHH)的模型肽时,观察到发射荧光显著增强(Φ = 0.60)。NiLODCF 和 H6Y1 之间的三元复合物的化学计量为 1:1。荧光强度随着 H6Y1 浓度的增加而增加,解离常数(Kd)被测定为 24 ± 1 µM,与 Ni-NTA 复合物和 His6 融合蛋白的解离常数(Kd = 1-20 µM)一致。这些结果表明,大环 NiLO 可作为多组氨酸序列的新型结合位点,NiLODCF 将适用于此类 His 标记蛋白质的可切换荧光探针。