人参皂苷Rh2与血清白蛋白相互作用立体选择性的光谱及分子对接研究

立体化学是影响外源性药物与生物功能大分子相互作用的关键结构因素。人参皂苷Rh2具有抗肿瘤等生理活性，已发现其中的C-20立体化学与多种生物学效应有关，但其与体内重要药物载体血清白蛋白(SA)相互作用的立体选择性研究鲜见报道。为此，采用紫外吸收光谱、荧光光谱、同步荧光光谱和分子对接技术，研究人参皂苷Rh2的C-20差向异构体在模拟生理条件下与SA相互作用的立体选择性特点及其机制。20S-和20R-Rh2均能与SA按摩尔比1∶1自发形成稳定的复合物，主要通过氢键和疏水相互作用，使SA的相关发光基团疏水性增强，同时改变Trp，Tyr等氨基酸残基周围微环境，从而影响紫外光谱特征吸收峰的位置和强度，并引起内源荧光的静态猝灭。二者与SA的相互作用特征及结合模式均存在显著差异，突出表现为结合区域以及参与氢键和疏水相互作用的基团和氨基酸残基数目及类别明显不同，20S-Rh2具有相对更高的结合常数和结合自由能。人参皂苷Rh2与血清白蛋白的相互作用具有立体选择性，C-20立体化学差异是其中的重要机制。

Study of Stereoselective Interaction Between Ginsenoside Rh2 and Serum Albumin by Spectroscopic Methods and Molecular Docking

Stereochemistry plays an important role in the interactions between functional bio-macromolecules and exogenous small-molecule drugs. Ginsenoside Rh2 is an effective constituent of ginseng with chirality of hydroxyl group at carbon-20, which has been found closely related to its multiple biological effects such as anti-tumor activity. However, the stereoselectivity of ginsenoside Rh2 interacting with serum albumin (SA), a vital drug carrier in the body, has been rarely reported. In the present study, interactions between SA and the C-20 eipmers of ginsenoside Rh2 were investigated under simulative physiological condition by molecular docking method and spectroscopic analyses, including UV absorption, fluorescence and synchronous fluorescence spectroscopy. Results showed that both 20S- and 20R-Rh2 could form 1∶1 type non-covalent complex with SA mainly via hydrogen bond and hydrophobic forces. According to the influence on spectra of SA, both epimers led to some increase in hydrophobicity for the light emitting residues of SA, as well as the change in micro-environment around some residues (including tyrosine and tryptophan) responsible for intrinsic fluorescence of SA, and fluorescence quenching mainly by a static mode. However, 20S-Rh2 displayed relatively larger binding constant and free energy in contrast with 20R-Rh2, suggesting stereoselective characteristics of the eipmers. The stereo-selectivity of ginsenoside Rh2 interacted with serum albumin may be related with stereochemistry of C-20.