Amphipols (a
portmanteau
In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together. of
amphiphilic
In chemistry, an amphiphile (), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'', nonpolar) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic c ...
polymers
A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...
) are a class of amphiphilic polymers designed to keep
membrane protein
Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
s soluble in water without the need for
detergents, which are traditionally used to this end but tend to be denaturing.
Amphipols adsorb onto the hydrophobic transmembrane surface of membrane proteins thanks to their hydrophobic moieties and keep the complexes thus formed water-soluble thanks to the hydrophilic ones. Amphipol-trapped membrane proteins are, as a rule, much more stable than detergent-solubilized ones, which facilitates their study by most biochemical and biophysical approaches. Amphipols can be used to fold denatured membrane proteins to their native form and have proven particularly precious in the field of
single-particle electron cryo-microscopy (
cryo-EM
Cryogenic electron microscopy (cryo-EM) is a transmission electron microscopy technique applied to samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An ...
; see ''e.g.'' ).The properties and uses of amphipols and other non-conventional surfactants are the subject of a book by Jean-Luc Popot.
[Popot, J.-L. (2018) Membrane proteins in aqueous solutions. From detergents to amphipols. ''Springer'', New York, xxv + 708 p.]
See also
*
Peptitergents - synthetic peptide sequences which can substitute to detergents to keep membrane proteins water-soluble.
*
Nanodisc
A nanodisc is a synthetic model membrane system which assists in the study of membrane proteins. Nanodiscs are discoidal proteins in which a lipid bilayer is surrounded by molecules that are amphipathic molecules including proteins, peptides, and ...
- water-soluble protein-stabilized lipid discs that can trap and stabilize membrane proteins.
References
Surfactants
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