Amphipols

{{Short description|Amphiphilic polymers}}

Amphipols (a portmanteau of amphiphilic polymers) are a class of amphiphilic polymers designed to keep membrane proteins soluble in water without the need for detergents, which are traditionally used to this end but tend to be denaturing.{{cite journal|last1=Bowie|first1=J|year=2001|title=Stabilizing membrane proteins|journal=Current Opinion in Structural Biology|volume=11|issue=4|pages=397–402|doi=10.1016/S0959-440X(00)00223-2|pmid=11495729|issn=0959-440X}} 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.{{cite journal|last1=Tribet|first1=C|last2=Audebert|first2=R|last3=Popot|first3=JL|date=24 December 1996|title=Amphipols: polymers that keep membrane proteins soluble in aqueous solutions.|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=93|issue=26|pages=15047–50|bibcode=1996PNAS...9315047T|doi=10.1073/pnas.93.26.15047|pmc=26353|pmid=8986761|doi-access=free}} 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. Popot, J.-L., et al. (2011) Amphipols from A to Z. Annu. Rev. Biophys. 40:379-408.Zoonens, M., Popot, J.-L. (2014) Amphipols for each season. J. Membr. Biol. 247:759-796.Popot, J.-L. (2018) Membrane proteins in aqueous solutions: From detergents to amphipols. Springer, New York, in the press. Amphipols can be used to fold denatured membrane proteins to their native formPocanschi, C.L., Dahmane, T., Gohon, Y., Rappaport, F., Apell, H.-J., Kleinschmidt, J.H., Popot, J.-L. (2006) Amphipathic polymers: tools to fold integral membrane proteins to their active form. Biochemistry 45:13954-13961.Dahmane, T., Damian, M., Mary, S., Popot, J.-L., Banères, J.-L. (2009) Amphipol-assisted in vitro folding of G protein-coupled receptors. Biochemistry 48:6516-6521. and have proven particularly precious in the field of single-particle electron cryo-microscopy (cryo-EM; see e.g. Althoff, T., Mills, D.J., Popot, J.-L., Kühlbrandt, W. (2011) Assembly of electron transport chain components in bovine mitochondrial supercomplex I1III2IV1. EMBO J. 30:4652-4664.Liao, M., Cao, E., Julius, D., Cheng, Y. (2013) Structure of the TRPV1 ion channel determined by electron cryo-microscopy. Nature 504:107-112.).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.