Partitioning of 2,6-Bis(1H-Benzimidazol-2-yl)pyridine fluorophore into a phospholipid bilayer: complementary use of fluorescence quenching studies and molecular dynamics simulations.
Partitioning of 2,6-Bis(1H-Benzimidazol-2-yl)pyridine fluorophore into a phospholipid bilayer: complementary use of fluorescence quenching studies and molecular dynamics simulations.
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DOI：
10.1016/j.bpc.2010.12.001
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发表时间：
2011-02
影响因子：
3.8
通讯作者：
Doroshenko, Andrey O.
中科院分区：
文献类型：
--
作者：
Kyrychenko, Alexander;Sevriukov, Igor Yu;Syzova, Zoya A.;Ladokhin, Alexey S.;Doroshenko, Andrey O.
关键词：
成功地使用荧光传感在阐明生物物理性质的脂膜需要的知识的分布和位置的发射分子在双层。我们在这里报告，2，6-双（1H-苯并咪唑-2-基）吡啶（BBP），这是几乎无荧光的水溶液中，揭示了强烈的发射增强在疏水环境中的磷脂双层，使其有趣的荧光探测的水含量在脂质膜。比较BBP在各种溶剂中的荧光行为与磷脂囊泡中的荧光行为，我们认为BBP荧光团和水分子之间的氢键相互作用在所观察到的“光开关效应”中起着至关重要的作用。因此，膜内水诱导荧光猝灭的损失被认为是由于BBP深入渗透到双层的疏水无水区域。在溶液中的过渡金属离子的强猝灭的特点，BBP也表现出显着的屏蔽的存在下，磷脂囊泡的猝灭剂的作用。我们使用在用脂质囊泡滴定探针分子时测量的荧光强度的增加来估计BBP从水性缓冲液转移到膜中的分配常数和吉布斯自由能（ΔG）。分配BBP显示非常有利的ΔG，其仅轻微地取决于双层的脂质组成，在-6.5至-7.0 kcal/mol的范围内变化。为了在分子水平上阐明探针与膜的结合相互作用，使用两种不同的方法通过原子分子动力学（MD）模拟对BBP在POPC双层中的分布和有利位置进行建模：（i）自由的、扩散驱动的探针分子到双层中的分配和（ii）染料分子穿过双层的渗透分布的受约束的伞形采样。这两种MD方法都同意关于BBP荧光团在双层的界面区域内的优选位置，位于烃酰基尾和脂质头基的初始部分之间。MD模拟还揭示了限制渗透性的水分子进入该区域的POPC双层，确定实验观察到的膜分区形式的BBP的强荧光增强。
Successful use of fluorescence sensing in elucidating the biophysical properties of lipid membranes requires knowledge of the distribution and location of an emitting molecule in the bilayer. We report here that 2,6-bis(1H-benzimidazol-2-yl)pyridine (BBP), which is almost non-fluorescent in aqueous solutions, reveals a strong emission enhancement in a hydrophobic environment of a phospholipid bilayer, making it interesting for fluorescence probing of water content in a lipid membrane. Comparing the fluorescence behavior of BBP in a wide variety of solvents with those in phospholipid vesicles, we suggest that the hydrogen bonding interactions between a BBP fluorophore and water molecules play a crucial role in the observed “light switch effect”. Therefore, the loss of water-induced fluorescence quenching inside a membrane are thought to be due to deep penetration of BBP into the hydrophobic, water-free region of a bilayer. Characterized by strong quenching by transition metal ions in solution, BBP also demonstrated significant shielding from the action of the quencher in the presence of phospholipid vesicles. We used the increase in fluorescence intensity, measured upon titration of probe molecules with lipid vesicles, to estimate the partition constant and the Gibbs free energy (ΔG) of transfer of BBP from aqueous buffer into a membrane. Partitioning BBP revealed strongly favorable ΔG, which depends only slightly on the lipid composition of a bilayer, varying in a range from -6.5 to -7.0 kcal/mol. To elucidate the binding interactions of the probe with a membrane on the molecular level, a distribution and favorable location of BBP in a POPC bilayer were modeled via atomistic molecular dynamics (MD) simulations using two different approaches: (i) free, diffusion-driven partitioning of the probe molecules into a bilayer and (ii) constrained umbrella sampling of a penetration profile of the dye molecule across a bilayer. Both of these MD approaches agreed with regard to the preferred location of a BBP fluorophore within the interfacial region of a bilayer, located between the hydrocarbon acyl tails and the initial portion of the lipid headgroups. MD simulations also revealed restricted permeability of water molecules into this region of a POPC bilayer, determining the strong fluorescence enhancement observed experimentally for the membrane-partitioned form of BBP.
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