DMPC vesicle structure and dynamics in the presence of low amounts of the saponin aescin

Abstract

Vesicle shape and bilayer parameters are studied by small-angle X-ray (SAXS) and small-angle neutron (SANS) scattering in the presence of the saponin aescin. We confirm successful incorporation of aescin molecules by analysis of the radii of gyration RG and study furthermore the impact of aescin incorporation on bilayer thickness parameters from the neutron and X-ray perspective. Additionally, the bending elasticity (κ) of these 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicle bilayers is studied in the presence of aescin. Neutron spin-echo spectroscopy (NSE) allows to detect subtle changes in the dynamics and κ of lipid membranes. Changes of κ are detectable at temperatures below and above the main phase transition temperature Tm of the lipid. The impact of aescin is much more significant below Tm. It has been found that below Tm the addition of aescin to the vesicles decreases the value of κ and softens the bilayer. Above Tm the value of κ increases with increasing aescin content and the bilayer becomes more rigid. Altogether, we demonstrate by analysis of the structure and dynamics of the vesicles that the impact of aescin strongly depends on the lipid state. Below Tm the membrane becomes fluidized and softer, above Tm solidified and stiffer compared to a DMPC membrane without additive at similar conditions.

Self-Assembly of the Bio-Surfactant Aescin in Solution: A Small-Angle X-ray Scattering and Fluorescence Study

“…Effects directly related to the interaction of aescin with the membranes of the cells contained in the veins have not been mentioned in this context so far. Nevertheless, it is known that aescin interacts with lipid membranes [18,[39][40][41], but the physico-chemical interaction on the molecular scale is still not fully understood. However, the behavior of aescin in solution, especially above the cmc, is essential to elucidate the structure-activity relationship with lipid membranes and the mechanism of action of aescin.…”

The Biosurfactant β-Aescin: A Review on the Physico-Chemical Properties and Its Interaction with Lipid Model Membranes and Langmuir Monolayers

“…The successful incorporation of β-aescin into the bilayer of the samples prepared as mentioned above was shown by a changing cross-sectional electron density profile of samples with varying β-aescin concentration obtained from SAXS measurements [47].…”

“…The interaction of β-aescin with bare lipid model membranes from the physicochemical perspective is subject of works published over the last 2 years by Sreij et al [46][47][48] and Geisler et al [49]. The work is done exemplarily on phospholipid bilayers composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at constant environmental conditions, i.e., in 50 mM phosphate buffer at physiological p(H)≈ p(D) of about 7.4 and a DMPC mass concentration of w(DMPC) = 15 mg/mL.…”

“…An overall summary of the concentration-dependent interactions and structures formed is illustrated schematically in Figure 8. At low β-aescin contents (region I) which ranges up to ≈0.8 mol%, β-aescin can be incorporated into stable SUVs and the structural parameters of these SUVs were studied by small-angle scattering with X-rays (SAXS) and neutrons (SANS) [47]. It was found that β-aescin incorporation leads to higher radii of gyration (R G ) with rising β-aescin content while the vesicles temperature-driven phase transition due to the conformational transition of DMPC's alkyl chains remains conserved.…”

“…Membrane dynamics affected by the incorporation of β-aescin were addressed by Sreij et al [47] by means of neutron spin-echo spectroscopy (NSE) measurements for DMPC SUVs in the mentioned β-aescin content regime. For β-aescin, the bilayer bending modulus κ depends on β-aescin concentration and lipid phase state.…”