SMALPs Are Not Simply Nanodiscs: The Polymer-to-Lipid Ratios of Fractionated SMALPs Underline Their Heterogeneous Nature
SMALPs Are Not Simply Nanodiscs: The Polymer-to-Lipid Ratios of Fractionated SMALPs Underline Their Heterogeneous Nature
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DOI：
10.1021/acs.biomac.3c00034
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发表时间：
2023-03-22
影响因子：
6.2
通讯作者：
Liang，Hongjun
中科院分区：
文献类型：
--
作者：
Kamilar，Elizabeth;Bariwal，Jitender;Liang，Hongjun
两亲性苯乙烯-马来酸（SMA）共聚物直接将生物膜溶解成SMA-脂质颗粒或SMALP，其通常被认为是纳米盘并被誉为天然膜平台。SMALP的前景光明，激发了许多SMA样共聚物的发现，这些共聚物也将生物膜溶解成推定的纳米盘，但一个根本问题仍然是SMALP或SMALP类似物在多大程度上真正类似于纳米盘的双层结构。这种不幸的模糊性破坏了SMA或SMA样共聚物在膜生物学中的效用，因为许多膜蛋白的结构和功能严重依赖于它们周围的基质。在这里，我们报告的SMALPs的结构异质性揭示通过分馏SMALPs组成的脂质和明确的SMA通过尺寸排阻色谱法，然后通过定量测定的聚合物-脂质（P/L）的化学计量比在个别馏分。通过P/L化学计量比的透镜，推测了不同的聚合物-脂质自组装纳米结构，如聚合物重塑的脂质体、聚合物包裹的纳米盘、聚合物-脂质混合胶束和脂质掺杂的聚合物胶束聚集体。我们将SMALP的结构异质性归因于单个聚合物链之间的微观结构变化，从而产生其多分散去污力。作为一个例子，我们证明了SMA具有相似的S/MA比，但不同的链大小优先参与不同的聚合物-脂质纳米结构。我们进一步证明，蛋白视紫红质，光驱动的质子泵溶解在相同的SMALP之间分布不同的自组装纳米结构，以显示不同的光循环动力学。我们的发现挑战了SMALP或SMALP类似物的天然纳米盘概念，并强调了在膜生物学研究中分离和鉴定结构不同的聚合物-脂质颗粒的必要性。
Amphipathic styrene-maleic acid (SMA) copolymers directly solubilize biomembranes into SMA-lipid particles, or SMALPs, that are often regarded as nanodiscs and hailed as a native membrane platform. The promising outlook of SMALPs inspires the discovery of many SMA-like copolymers that also solubilize biomembranes into putative nanodiscs, but a fundamental question remains on how much the SMALPs or SMALP analogues truly resemble the bilayer structure of nanodiscs. This unfortunate ambiguity undermines the utility of SMA or SMA-like copolymers in membrane biology because the structure and function of many membrane proteins depend critically on their surrounding matrices. Here, we report the structural heterogeneity of SMALPs revealed through fractionating SMALPs comprised of lipids and well-defined SMAs via size-exclusion chromatography followed by quantitative determination of the polymer-to-lipid (P/L) stoichiometric ratios in individual fractions. Through the lens ofP/Lstoichiometric ratios, different self-assembled polymer–lipid nanostructures are inferred, such as polymer-remodeled liposomes, polymer-encased nanodiscs, polymer–lipid mixed micelles, and lipid-doped polymer micellar aggregates. We attribute the structural heterogeneity of SMALPs to the microstructure variations amongst individual polymer chains that give rise to their polydisperse detergency. As an example, we demonstrate that SMAs with a similarS/MA ratio but different chain sizes participate preferentially in different polymer–lipid nanostructures. We further demonstrate that proteorhodopsin, a light-driven proton pump solubilized within the same SMALPs is distributed amongst different self-assembled nanostructures to display different photocycle kinetics. Our discovery challenges the native nanodisc notion of SMALPs or SMALP analogues and highlights the necessity to separate and identify the structurally dissimilar polymer–lipid particles in membrane biology studies.