specifically designed with membrane biology in sight. Comparing the effects of a series of well-defined
detergents on the stability and functionality of MPs led to a better understanding of the structural
parameters that contribute to make a detergent more or less destabilizing. As a result of this feedback,
“milder” detergents were designed, synthesized, and validated, a process that continues to this day. In
the course of these studies, it was realized that a major source of destabilization is that detergents tend
to strip MPs off the lipids with which they are naturally associated. This initiated, starting essentially in
the 1990s, attempts to replace the detergent environment with one that would be less aggressive.
MPs are naturally amphipathic, meaning that some of their surface is adapted to being solvated
by water, some to being immersed in the highly hydrophobic membrane interior, where it is in intimate
contact either with other MPs or with the hydrophobic moieties of lipids – most often with both.
Making MPs water-soluble implies to cover these hydrophobic surfaces with a layer of surfactant, the
hydrophobic moieties of which adsorb onto the protein, while the hydrophilic ones ensure the interface
with water. Such is the role of detergents. Doing away with detergents imposes to replace them with
other surfactants. One solution is to reinsert MPs into lipid vesicles or planar lipid films. This
reconstitutes an environment that is similar to the native one, and is in general stabilizing. The large
objects thus obtained are suitable for many functional studies, but neither for purification nor for most
structural approaches. Non-detergent – “nonconventional” – media that complex MPs to form small
(nanometric) particles are the main subject of this book. They include, in the order of their apparition
on the biochemist’s bench, detergent-stabilized lipid discs (“bicelles”), amphipathic peptides, amphipathic polymers (“amphipols”), fluorinated surfactants, protein-stabilized lipid discs (“nanodiscs”),
etc., the properties, advantages, and limitations of all of which will be discussed in turn.
The book starts with a presentation of membrane proteins in their natural medium, with a
discussion of their functions, their structure, the forces that stabilize them, and the interactions that
they establish with their environment, in particular with lipids (Chap. 1). In Chap. 2, we consider the
traditional approach to solubilizing MPs and handling them in aqueous solutions, namely the use
of detergents, including a discussion on the mechanisms by which detergents destabilize (or are
hypothesized to destabilize) MPs and a presentation of recently developed detergents. Chapter 3
introduces the various nonconventional approaches that have been developed, with an examination
of which applications they are best suited to. Bicelles, nanodiscs, amphipathic peptides, and fluorinated
surfactants are discussed in this chapter.
We then turn to amphipols. Chapter 4 describes their chemical structure, their synthesis, and
their chemical-physical properties, with the stress put on their solution behavior. Chapter 5 examines
the various ways to trap MPs with amphipols and the structure and properties of MP/amphipol
complexes, the knowledge of which is essential to developing their applications in basic research,
medicine, and the industry. Chapters 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 then discuss in turn each
application that has been or is being validated: MP folding and in vitro synthesis, optical spectroscopy
and solution studies, NMR, crystallography, electron microscopy, immobilization of MPs onto solid
supports, mass spectrometry, and biomedical applications. Each chapter starts with a self-contained
presentation of the principles of the technique to be discussed and the state of the art when applied to
detergent-solubilized MPs, which should make it accessible even to readers with no familiarity with
the approach considered. It comprises thematic tables that organize an exhaustive review of the
literature so as to make it straightforward for the experimenter to identify those publications most
relevant to her/his goals. Most technical chapters include one or several protocols, prepared and
commented by experts in the use of amphipols for the application considered. Suggestions and
speculations about future developments are offered at the end of each chapter and some more general
comments at the end of the book.
xii
Preface
detergents on the stability and functionality of MPs led to a better understanding of the structural
parameters that contribute to make a detergent more or less destabilizing. As a result of this feedback,
“milder” detergents were designed, synthesized, and validated, a process that continues to this day. In
the course of these studies, it was realized that a major source of destabilization is that detergents tend
to strip MPs off the lipids with which they are naturally associated. This initiated, starting essentially in
the 1990s, attempts to replace the detergent environment with one that would be less aggressive.
MPs are naturally amphipathic, meaning that some of their surface is adapted to being solvated
by water, some to being immersed in the highly hydrophobic membrane interior, where it is in intimate
contact either with other MPs or with the hydrophobic moieties of lipids – most often with both.
Making MPs water-soluble implies to cover these hydrophobic surfaces with a layer of surfactant, the
hydrophobic moieties of which adsorb onto the protein, while the hydrophilic ones ensure the interface
with water. Such is the role of detergents. Doing away with detergents imposes to replace them with
other surfactants. One solution is to reinsert MPs into lipid vesicles or planar lipid films. This
reconstitutes an environment that is similar to the native one, and is in general stabilizing. The large
objects thus obtained are suitable for many functional studies, but neither for purification nor for most
structural approaches. Non-detergent – “nonconventional” – media that complex MPs to form small
(nanometric) particles are the main subject of this book. They include, in the order of their apparition
on the biochemist’s bench, detergent-stabilized lipid discs (“bicelles”), amphipathic peptides, amphipathic polymers (“amphipols”), fluorinated surfactants, protein-stabilized lipid discs (“nanodiscs”),
etc., the properties, advantages, and limitations of all of which will be discussed in turn.
The book starts with a presentation of membrane proteins in their natural medium, with a
discussion of their functions, their structure, the forces that stabilize them, and the interactions that
they establish with their environment, in particular with lipids (Chap. 1). In Chap. 2, we consider the
traditional approach to solubilizing MPs and handling them in aqueous solutions, namely the use
of detergents, including a discussion on the mechanisms by which detergents destabilize (or are
hypothesized to destabilize) MPs and a presentation of recently developed detergents. Chapter 3
introduces the various nonconventional approaches that have been developed, with an examination
of which applications they are best suited to. Bicelles, nanodiscs, amphipathic peptides, and fluorinated
surfactants are discussed in this chapter.
We then turn to amphipols. Chapter 4 describes their chemical structure, their synthesis, and
their chemical-physical properties, with the stress put on their solution behavior. Chapter 5 examines
the various ways to trap MPs with amphipols and the structure and properties of MP/amphipol
complexes, the knowledge of which is essential to developing their applications in basic research,
medicine, and the industry. Chapters 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 then discuss in turn each
application that has been or is being validated: MP folding and in vitro synthesis, optical spectroscopy
and solution studies, NMR, crystallography, electron microscopy, immobilization of MPs onto solid
supports, mass spectrometry, and biomedical applications. Each chapter starts with a self-contained
presentation of the principles of the technique to be discussed and the state of the art when applied to
detergent-solubilized MPs, which should make it accessible even to readers with no familiarity with
the approach considered. It comprises thematic tables that organize an exhaustive review of the
literature so as to make it straightforward for the experimenter to identify those publications most
relevant to her/his goals. Most technical chapters include one or several protocols, prepared and
commented by experts in the use of amphipols for the application considered. Suggestions and
speculations about future developments are offered at the end of each chapter and some more general
comments at the end of the book.
xii
Preface