Amphipol-Mediated
Immobilization of Membrane
Proteins and Its Applications
13
Summary
Tagged amphipols (APols) are obtained by chemically grafting APols with moieties
that can interact with specific partners. They combine in a single molecule three highly
useful properties: keeping membrane proteins (MPs) water-soluble, stabilizing them,
and functionalizing them. MPs trapped with tagged APols can be attached to solid
supports and other scaffolds in a gentle, non-covalent but permanent manner, without
interacting themselves with the support nor having to be genetically nor chemically
modified. Furthermore, a single tagged APol can be used for any number of MPs.
Three types of tags have been thoroughly validated to date – biotin, polyhistidine, and
an oligonucleotide – and three more are under development, randomly distributed
imidazoles, sulfides, and sulfhydrides. Between them, they cover a very broad range of
properties, from low to extremely high affinity and from easy reversibility to nearirreversibility. They have been applied to immobilizing membrane proteins onto a
variety of supports, including avidin-coated or nucleotide-bearing beads, chips, and
culture plates. MPs immobilized via tagged APols remain native and functional and
can be recognized by ligands big and small, such as antibodies, toxins, or neurotransmitter analogs, which can be directly or indirectly detected by such methods as surface
plasmon resonance (SPR) and fluorescence microscopy. They have been used to select
protein binders and to study the interaction of a bacterial outer membrane protein with
a bacteriophage tail protein. They lend themselves well to multiplexing approaches
permitting to immobilize multiple membrane proteins at defined positions onto chips or
electrodes. Tagged APols have other possible applications, e.g. in structural biology
and for medical uses.
13.1 Introduction
One of the most useful characteristics of amphipols (APols) is that, at variance with detergents, they do
not spontaneously desorb from the transmembrane (TM) surface of the membrane proteins (MPs) they
keep water-soluble: APols can be readily removed, but they have to be exchanged for another
surfactant, such as a detergent or another APol (Chap. 5, § 5.7). In solution, extensive washing with
# Springer International Publishing AG, part of Springer Nature 2018
J. -L. Popot, Membrane Proteins in Aqueous Solutions, Biological and Medical Physics,
Biomedical Engineering, https://doi.org/10.1007/978-3-319-73148-3_13
591
Immobilization of Membrane
Proteins and Its Applications
13
Summary
Tagged amphipols (APols) are obtained by chemically grafting APols with moieties
that can interact with specific partners. They combine in a single molecule three highly
useful properties: keeping membrane proteins (MPs) water-soluble, stabilizing them,
and functionalizing them. MPs trapped with tagged APols can be attached to solid
supports and other scaffolds in a gentle, non-covalent but permanent manner, without
interacting themselves with the support nor having to be genetically nor chemically
modified. Furthermore, a single tagged APol can be used for any number of MPs.
Three types of tags have been thoroughly validated to date – biotin, polyhistidine, and
an oligonucleotide – and three more are under development, randomly distributed
imidazoles, sulfides, and sulfhydrides. Between them, they cover a very broad range of
properties, from low to extremely high affinity and from easy reversibility to nearirreversibility. They have been applied to immobilizing membrane proteins onto a
variety of supports, including avidin-coated or nucleotide-bearing beads, chips, and
culture plates. MPs immobilized via tagged APols remain native and functional and
can be recognized by ligands big and small, such as antibodies, toxins, or neurotransmitter analogs, which can be directly or indirectly detected by such methods as surface
plasmon resonance (SPR) and fluorescence microscopy. They have been used to select
protein binders and to study the interaction of a bacterial outer membrane protein with
a bacteriophage tail protein. They lend themselves well to multiplexing approaches
permitting to immobilize multiple membrane proteins at defined positions onto chips or
electrodes. Tagged APols have other possible applications, e.g. in structural biology
and for medical uses.
13.1 Introduction
One of the most useful characteristics of amphipols (APols) is that, at variance with detergents, they do
not spontaneously desorb from the transmembrane (TM) surface of the membrane proteins (MPs) they
keep water-soluble: APols can be readily removed, but they have to be exchanged for another
surfactant, such as a detergent or another APol (Chap. 5, § 5.7). In solution, extensive washing with
# Springer International Publishing AG, part of Springer Nature 2018
J. -L. Popot, Membrane Proteins in Aqueous Solutions, Biological and Medical Physics,
Biomedical Engineering, https://doi.org/10.1007/978-3-319-73148-3_13
591