Changes in membrane elasticity caused by the hydrophobic surfactant proteins correlate poorly with adsorption of lipid vesicles,Soft Matter

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Changes in membrane elasticity caused by the hydrophobic surfactant proteins correlate poorly with adsorption of lipid vesicles
Soft Matter ( IF 2.9 ) Pub Date : 2021-2-17 , DOI: 10.1039/d0sm02223c
Ryan W Loney ₁ , Bret Brandner , Maayan P Dagan , Paige N Smith , Megan Roche , Jonathan R Fritz , Stephen B Hall , Stephanie A Tristram-Nagle

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To establish how the hydrophobic surfactant proteins, SP-B and SP-C, promote adsorption of lipids to an air/water interface, we used X-ray diffuse scattering (XDS) to determine an order parameter of the lipid chains (S_xray) and the bending modulus of the lipid bilayers (K_C). Samples contained different amounts of the proteins with two sets of lipids. Dioleoylphosphatidylcholine (DOPC) provided a simple, well characterized model system. The nonpolar and phospholipids (N&PL) from extracted calf surfactant provided the biological mix of lipids. For both systems, the proteins produced changes in S_xray that correlated well with K_C. The dose–response to the proteins, however, differed. Small amounts of protein generated large decreases in S_xray and K_C for DOPC that progressed monotonically. The changes for the surfactant lipids were erratic. Our studies then tested whether the proteins produced correlated effects on adsorption. Experiments measured the initial fall in surface tension during adsorption to a constant surface area, and then expansion of the interface during adsorption at a constant surface tension of 40 mN m⁻¹. The proteins produced a sigmoidal increase in the rate of adsorption at 40 mN m⁻¹ for both lipids. The results correlated poorly with the changes in S_xray and K_C in both cases. Disordering of the lipid chains produced by the proteins, and the softening of the bilayers, fail to explain how the proteins promote adsorption of lipid vesicles.

中文翻译：

疏水性表面活性剂蛋白引起的膜弹性变化与脂质囊泡的吸附相关性较差

为了确定疏水性表面活性剂蛋白 SP-B 和 SP-C 如何促进脂质吸附到空气/水界面，我们使用 X 射线漫散射 (XDS) 来确定脂质链的有序参数 ( S _xray )和脂质双层的弯曲模量 ( K _C )。样品含有不同量的蛋白质和两组脂质。二油酰磷脂酰胆碱 (DOPC) 提供了一个简单、特征良好的模型系统。从小牛表面活性剂中提取的非极性和磷脂 (N&PL) 提供了脂质的生物混合物。对于这两个系统，蛋白质产生的S _{x 射线}变化与K _C密切相关。然而，蛋白质的剂量反应有所不同。少量蛋白质会导致 DOPC 的S _{x 射线}和K _C大幅降低，且单调进行。表面活性剂脂质的变化不稳定。然后我们的研究测试了蛋白质是否对吸附产生相关影响。实验测量了吸附至恒定表面积过程中表面张力的初始下降，以及随后在40 mN m ^-1的恒定表面张力下吸附过程中界面的扩展。蛋白质在 40 mN m ^-1下对两种脂质的吸附速率均产生 S 形增加。在这两种情况下，结果与S _{x 射线}和K _C的变化相关性较差。蛋白质产生的脂质链的紊乱以及双层的软化无法解释蛋白质如何促进脂质囊泡的吸附。

更新日期：2021-02-25

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