Amphiphol

Amphiphol is a term sometimes used to describe amphipols, a class of synthetic amphiphilic polymers designed to solubilize and stabilize membrane proteins in aqueous solutions. The spelling amphiphol is less common than amphipol, and some sources treat it as an informal variant. Amphipols differ from detergents in that they form a continuous polymeric belt around the hydrophobic surface of a membrane protein, promoting solubility without the need for micelles.

Most amphipols are based on a hydrophilic polymer backbone bearing hydrophobic grafts or side chains that provide a compatible interface with the protein’s transmembrane regions. In solution, they bind to membrane proteins after detergent removal, yielding small, single-particle complexes that remain stable across a range of pH and salt conditions. This stability can help preserve native-like conformations during downstream analyses.

Applications of amphipols are primarily in membrane protein structural biology. They are used to solubilize, stabilize, and crystallize membrane proteins for techniques such as cryo-electron microscopy, X-ray crystallography, and NMR. Typical workflows include initial extraction with a detergent, followed by exchange to an amphipol through detergent removal methods such as adsorption with Biobeads or dialysis.

Advantages of amphipols include enhanced long-term stability, compatibility with multiple structural methods, and reduced aggregation compared with some detergents. Limitations include that not all proteins tolerate amphipols well, potential interference with certain analyses, and the need for careful optimization of polymer type and protein–polymer ratio. Production and availability can also vary by supplier.

See also: amphipol derivatives such as A8-35 and other polyamphiphilic systems; comparisons with detergents and other solubilization strategies for membrane proteins.