Preface
Articles and reviews dealing with membrane proteins typically start with the following four statements:
(i) Membranes are an essential feature of living matter, playing key roles in compartmenting
it and controlling exchanges of matter and information between and within cells.
(ii) Genes encoding transmembrane proteins (hereafter “membrane proteins,” MPs) make up
about one-third of genomes.
(iii) Our knowledge of the structure and function of MPs is essential both to understanding cell
physiology and to controlling it; it is an absolute requirement in order to develop more
efficient drugs, a majority of which have MPs as their target.
(iv) Yet this knowledge lags way behind that of soluble proteins, because MPs are much more
difficult to produce, to purify, and to handle; as a result, MP structures, for instance, make
up only a minute fraction of those hosted by the Protein Data Bank.
All of this is true, and it has spurred massive efforts to develop MP-specific methodologies. As
will be seen in the course of this book, some of the results achieved are truly spectacular.
The central point we will tackle here is how to keep MPs in their native state after extracting
them from their original environment, a problem that has haunted many a graduate student and
prematurely aged many a principal investigator. Quite a few investigations can be carried out while
keeping the target MP in the membrane medium it has evolved to function in, be it in the whole
organism, in the cell, or in native membrane fragments. However, a detailed understanding of a MP’s
structure and function implies, in the quasi-totality of cases, to extract it from the membrane and to
purify and handle it in aqueous solutions, a medium it is not adapted to. “Extracting” involves
dispersing the molecules that make up a membrane, mainly lipids and proteins, so that they can be
separated one from another and the one relevant MP or MP complex purified. MPs and lipids,
however, are intimately associated in vivo. Dispersing them results, in nearly all cases, in the more
or less rapid inactivation of the target protein.
As will be recalled in Chap. 2 of this book, dispersion is traditionally achieved using detergents.
Detergents constitute a special class of surfactants – meaning, in our case, molecules with both
hydrophilic and hydrophobic moieties – characterized by their ability to solubilize fats. The first
detergents used in membrane biochemistry were industrial or natural detergents, and their use was
highly empirical. Starting in the 1970s, membrane biochemists introduced themselves more deeply to
the physical chemistry of surfactants, and in the 1980s organic chemists started synthesizing detergents
xi
Articles and reviews dealing with membrane proteins typically start with the following four statements:
(i) Membranes are an essential feature of living matter, playing key roles in compartmenting
it and controlling exchanges of matter and information between and within cells.
(ii) Genes encoding transmembrane proteins (hereafter “membrane proteins,” MPs) make up
about one-third of genomes.
(iii) Our knowledge of the structure and function of MPs is essential both to understanding cell
physiology and to controlling it; it is an absolute requirement in order to develop more
efficient drugs, a majority of which have MPs as their target.
(iv) Yet this knowledge lags way behind that of soluble proteins, because MPs are much more
difficult to produce, to purify, and to handle; as a result, MP structures, for instance, make
up only a minute fraction of those hosted by the Protein Data Bank.
All of this is true, and it has spurred massive efforts to develop MP-specific methodologies. As
will be seen in the course of this book, some of the results achieved are truly spectacular.
The central point we will tackle here is how to keep MPs in their native state after extracting
them from their original environment, a problem that has haunted many a graduate student and
prematurely aged many a principal investigator. Quite a few investigations can be carried out while
keeping the target MP in the membrane medium it has evolved to function in, be it in the whole
organism, in the cell, or in native membrane fragments. However, a detailed understanding of a MP’s
structure and function implies, in the quasi-totality of cases, to extract it from the membrane and to
purify and handle it in aqueous solutions, a medium it is not adapted to. “Extracting” involves
dispersing the molecules that make up a membrane, mainly lipids and proteins, so that they can be
separated one from another and the one relevant MP or MP complex purified. MPs and lipids,
however, are intimately associated in vivo. Dispersing them results, in nearly all cases, in the more
or less rapid inactivation of the target protein.
As will be recalled in Chap. 2 of this book, dispersion is traditionally achieved using detergents.
Detergents constitute a special class of surfactants – meaning, in our case, molecules with both
hydrophilic and hydrophobic moieties – characterized by their ability to solubilize fats. The first
detergents used in membrane biochemistry were industrial or natural detergents, and their use was
highly empirical. Starting in the 1970s, membrane biochemists introduced themselves more deeply to
the physical chemistry of surfactants, and in the 1980s organic chemists started synthesizing detergents
xi