Amphipols are short amphipatic polymers that are specifically designed to stabilize membrane proteins in aqueous solutions.
Due to their dense distribution of hydrophobic chains they tightly bind to transmembrane surfaces of membrane proteins and cover it with a thin interfacial layer of surfactant[1]. The resulting small hydrophilic complexes have several advantages over usually much larger protein detergent complexes, such as stability and functionality of the membrane protein.
Amphipol A8-35 is successfully applied as stabilizing agent in Cryo-EM[2-5] and X-ray crystallography[6].
[1] Zoonens et al. (2014) Amphipols for Each Season. J Membrane Biol 247:759.
[2] Chen et al. (2016) Structure of the STRA6 receptor for retinol uptake. Science 353:887.
[3] Zubcevic et al. (2016) Cryo-Electron Microscopy of the Trpv2 Ion Channel. Nat Struct Mol Biol 23:180.
[4] Bai et al. (2015) Sampling the conformational space of the catalytic subunit of human gamma-secretase. DOI 10.7554/eLife.11182.
[5] Althoff et al. (2011) Arrangement of electron transport chain components in bovine mitochondrial supercomplex I1III2IV1. EMBO J 30:4652.
[6] Polovinkin et al. (2014) High-Resolution Structure of a Membrane Protein Transferred from Amphipol to a Lipidic Mesophase. J Membrane Biol 247:997.