Faculty of Chemistry, Warsaw University of Technology , Noakowskiego 3, 00-664 Warsaw, Poland.
Max Planck Institute of Colloids and Interfaces , Science Park Potsdam-Golm, 14476 Potsdam, Germany.
Langmuir. 2017 Apr 18;33(15):3871-3881. doi: 10.1021/acs.langmuir.6b04613. Epub 2017 Apr 5.
Digitonin, a steroidal saponin obtained from the foxglove plant (Digitalis purpurea), displays a wide spectrum of biological properties and is often used as a model in mechanistic investigations of the biological activity of saponins. In the present study, Langmuir monolayers of zwitterionic (DPPC, DMPE, POPC, POPE, DSPC, DSPE, and DPPE) and ionic (DPPS and DPPG) phospholipids were employed in order to better understand the effect of digitonin on the lipid organization. For this purpose, a combination of surface pressure relaxation, infrared reflection absorption spectroscopy (IRRAS), and fluorescence microscopy measurements was used. The observed increase in surface pressure (Π) suggests that digitonin can adsorb at the air/water interface, both bare and covered with the uncompressed phospholipid monolayers. However, the detailed analysis of IRRAS and fluorescence microscopy data shows that digitonin interacts with the lipid monolayers in a very selective way, and both the headgroup and the lipid tails affect this interaction. Nevertheless, it should be noted that in no case did digitonin cause any disruptive effects on the monolayers. The DPPE and DPPS monolayers get disordered by penetration with digitonin, despite an increase in surface pressure, leading to an unprecedented LC-LE transition. Interestingly, saponin could be easily squeezed out of these monolayers by mechanical compression.
皂角苷是从毛地黄植物（Digitalis purpurea）中提取的一种甾体皂苷，具有广泛的生物学特性，常用于皂苷生物活性的机制研究。本研究采用两性离子（DPPC、DMPE、POPC、POPE、DSPC、DSPE 和 DPPE）和离子型（DPPS 和 DPPG）磷脂的朗缪尔单层膜来更好地理解皂角苷对脂质组织的影响。为此，我们结合表面压力弛豫、红外反射吸收光谱（IRRAS）和荧光显微镜测量来进行研究。观察到的表面压力（Π）增加表明皂角苷可以在空气/水界面上吸附，无论是在未压缩的磷脂单层膜上还是在其裸露状态下。然而，IRRAS 和荧光显微镜数据的详细分析表明，皂角苷以非常选择性的方式与脂质单层相互作用，其头部基团和脂质尾部都会影响这种相互作用。尽管如此，值得注意的是，皂角苷在任何情况下都不会对单层膜造成任何破坏作用。尽管表面压力增加，DPPE 和 DPPS 单层膜还是会因皂角苷的渗透而变得无序，导致前所未有的 LC-LE 转变。有趣的是，皂角苷可以很容易地被机械压缩从这些单层膜中挤出。
