Membrane proteins (MPs) are important pharmacological targets because of their involvement in many essential cellular processes whose dysfunction can lead to a large variety of diseases. A detailed knowledge of the structure of MPs and the molecular mechanisms of their activity is essential to the design of new therapeutic agents. However, studying MPs in vitro is challenging, because it generally implies their overexpression under a functional form, followed by their extraction from membranes and purification. Targeting an overexpressed MP to a membrane is often toxic and expression yields tend to be limited. One alternative is the formation of inclusion bodies (IBs) in the cytosol of the cell, from which MPs need then to be folded to their native conformation before structural and functional analysis can be contemplated. Folding MPs targeted to IBs is a difficult task. Specially designed amphipathic polymers called ‘amphipols’ (APols), which have been initially developed with the view of improving the stability of MPs in aqueous solutions compared to detergents, can be used to fold both α-helical and β-barrel MPs. APols represent an interesting novel amphipathic medium, in which high folding yields can be achieved. In this review, the properties of APol A8-35 and of the complexes they form with MPs are summarized. An overview of the most important studies reported so far using A8-35 to fold MPs is presented. Finally, from a practical point of view, a detailed description of the folding and trapping methods is given.

膜蛋白（MPs）是重要的药理学靶标，因为它们参与了许多重要的细胞过程，这些过程的功能障碍可能导致多种疾病。MP的结构及其活性的分子机制的详细知识对于设计新的治疗剂至关重要。但是，体外研究MPs之所以具有挑战性，是因为它通常暗示它们在功能形式下过度表达，然后从膜中提取并纯化。将过表达的MP靶向膜通常是有毒的，表达产量往往受到限制。一种替代方法是在细胞的细胞质中形成包涵体（IBs），然后可以从中折叠MP到其天然构象，然后才能进行结构和功能分析。折叠针对IB的MP是一项艰巨的任务。经过特殊设计的两亲聚合物称为“ amphipols”（APols），最初被开发出来的目的是与洗涤剂相比改善水溶液中MP的稳定性，可用于折叠α-螺旋和β-桶议员。APols代表了一种有趣的新型两亲性介质，在该介质中可以实现高折叠产量。在这篇综述中，对APol A8-35及其与MP形成的复合物的性质进行了总结。概述了迄今为止报道的使用A8-35折叠MP的最重要的研究。最后，从实用的角度，给出了折叠和陷印方法的详细描述。