Coimbra Chemistry Center-Institute of Molecular Sciences (CQC-IMS), University of Coimbra, 3004-535 Coimbra, Portugal.
Department of Chemistry, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal.
Molecules. 2022 Feb 19;27(4):1420. doi: 10.3390/molecules27041420.
rhodamines are dyes widely used as fluorescent tags in cell imaging, probing of mitochondrial membrane potential, and as P-glycoprotein model substrates. In all these applications, detailed understanding of the interaction between rhodamines and biomembranes is fundamental.
we combined atomistic molecular dynamics (MD) simulations and fluorescence spectroscopy to characterize the interaction between rhodamines 123 and B (Rh123 and RhB, respectively) and POPC bilayers.
while the xanthene moiety orients roughly parallel to the membrane plane in unrestrained MD simulations, variations on the relative position of the benzoic ring (below the xanthene for Rh123, above it for RhB) were observed, and related to the structure of the two dyes and their interactions with water and lipids. Subtle distinctions were found among different ionization forms of the probes. Experimentally, RhB displayed a lipid/water partition coefficient more than two orders of magnitude higher than Rh123, in agreement with free energy profiles obtained from umbrella sampling MD.
this work provided detailed insights on the similarities and differences in the behavior of bilayer-inserted Rh123 and RhB, related to the structure of the probes. The much higher affinity of RhB for the membranes increases the local concentration and explains its higher apparent affinity for P-glycoprotein reconstituted in model membranes.
罗丹明类染料被广泛用作细胞成像、线粒体膜电位探测以及 P-糖蛋白模型底物的荧光标记物。在所有这些应用中，深入了解罗丹明类染料与生物膜之间的相互作用是至关重要的。
我们结合原子分子动力学（MD）模拟和荧光光谱学来表征罗丹明 123（Rh123）和罗丹明 B（RhB）与 POPC 双层膜之间的相互作用。
在无约束的 MD 模拟中，吖啶部分大致平行于膜平面取向，但观察到苯甲酰环的相对位置（对于 Rh123 在吖啶环下方，对于 RhB 在其上方）发生变化，这与两种染料的结构及其与水和脂质的相互作用有关。探针的不同离解形式之间存在细微差别。实验上，RhB 的脂质/水分配系数比 Rh123 高出两个数量级以上，与从伞形采样 MD 获得的自由能图谱一致。
这项工作提供了关于插入双层膜的 Rh123 和 RhB 行为的相似性和差异性的详细见解，这与探针的结构有关。RhB 与膜的亲和力高得多，增加了局部浓度，并解释了它在模型膜中重组的 P-糖蛋白的表观亲和力更高的原因。
