N.G.Brady et al. SAXS Data of SMA Copolymers in Solution

Over the past decade, Styrene Maleic Acid Alternating Copolymers (SMA) have gained interest as an alternative to detergent solubilization for the isolation of membrane bound proteins. During the canonical method of membrane solubilization via surfactant-lipid exchange, detergents have been shown to replace membrane lipids peripheral and interior to membrane bound proteins [1]. For both the investigation of the proteolipid interface and the retention of native activity in vitro, the formation of SMA lipid particles (SMALPs) presents a novel opportunity to isolate the proximal membrane environment, encompassing and throughout membrane proteins in vitro. The mechanism by which SMA associates with the membrane resulting in SMALPs is unknown, leading to SMAs of differing physicochemical properties (styrene:maleic acid ratio and length of copolymer fragments) being reported as optimum for extraction of various membrane proteins. The coordinated supramolecular assembly of SMA amphiphilic copolymers free in solution has yet to be elucidated over a range of environmental conditions, which may be pertinent to the underlying mechanism of protein extraction by this method. This study investigates the shape and size of diverse SMA aggregates in solution at various pH, ionic strength, concentration and temperature, analyzed by small angle X-ray scattering. The SMA supramolecular aggregates exhibit similar prolate ellipsoidal geometry of varying size, dependent on the degree of hydrophobicity of the SMA copolymer. At elevated pH and temperature, particles composed of SMAs enriched in styrene undergo elongation at the poles, increasing in maximum particle diameter. The magnitude of this effect increases proportional to increasing length of the SMA copolymer fragments. Included here is all raw data for SAXS curves, Guinier approximation and distance distribution analyses.

过去十年间，苯乙烯马来酸交替共聚物（Styrene Maleic Acid Alternating Copolymers, SMA）作为去污剂增溶法的替代策略，在膜结合蛋白分离领域受到广泛关注。在经典的表面活性剂-脂质交换膜增溶流程中，去污剂可取代膜结合蛋白外周及内部区域的膜脂质[1]。无论是针对蛋白脂质界面的研究，还是体外天然活性的保留，SMA脂质颗粒（SMA lipid particles, SMALPs）的构建均为体外分离包含膜蛋白及其近端膜环境的完整体系提供了全新路径。

目前，SMA与膜结合并形成SMALPs的具体机制尚未阐明，因此不同理化性质（苯乙烯与马来酸摩尔比、共聚物片段长度）的SMA被陆续报道可最优分离不同种类的膜结合蛋白。溶液中游离的SMA两亲共聚物的协同超分子组装机制，在多种环境条件下仍未被明确解析，而这可能与该方法提取膜蛋白的核心作用机制密切相关。

本研究采用小角X射线散射（Small Angle X-ray Scattering, SAXS）技术，对不同pH、离子强度、样品浓度及温度条件下，溶液中多种SMA聚集体的形貌与尺寸进行了分析。结果表明，SMA超分子聚集体均呈现相似的长椭球几何结构，但其尺寸随SMA共聚物的疏水程度变化而发生改变。在高pH与高温条件下，苯乙烯富集型SMA形成的颗粒会出现极区伸长现象，导致最大粒径增大；且该效应的强度随SMA共聚物片段长度的增加呈正比提升。

本文附带了全部SAXS曲线、吉尼耶近似（Guinier approximation）分析及距离分布分析的原始数据。