The Use of Amphipols in Mass
Spectrometry
14
Summary
Mass spectrometry (MS) analyses of membrane proteins (MPs) have progressed
spectacularly over the past decade. Yet, the presence of detergents remains a source
of problems. In matrix-assisted laser desorption ionization (MALDI), only certain
detergents are acceptable, which are not necessarily those best tolerated by the
proteins under study. In electrospray ionization-mass spectrometry (ESI-MS) studies,
where MPs can be brought to the gas phase under their native oligomeric state and
conformation, a fine line has to be navigated between the Charybdis of retaining too
many detergent molecules, yielding unexploitable spectra, and the Scylla of using too
much collisional energy to strip away the detergent and denaturing the protein. The use
of amphipols (APols) as alternatives to detergents has been validated in these two
experimental configurations. MALDI-time-of-flight (TOF) experiments have been carried out using either A8-35 or non-ionic APols and have yielded mass determinations,
identification of posttranslational modifications and associated lipids, and sequence
data. In ESI-MS experiments, often combined with ion mobility (IM) measurements of
the collisional cross section of the protein, which yield information about its conformation, A8-35 has proven particularly convenient, protecting MPs against unfolding
better than the much used detergent dodecylmaltoside. Fast photochemical oxidation
has revealed details of the way the two surfactants interact with MPs that tally well with
the conclusions from molecular dynamics and NMR investigations. Whether APols can
be used to preserve the oligomeric state of MPs in the gas phase, however, is uncertain.
Finally, A8-35 has been used as a powerful tool to simplify whole proteome
investigations.
14.1 Introduction
The application of mass spectrometry (MS) to membrane proteins (MPs) is a relatively recent
development. As with most technologies, it has lagged behind application to soluble proteins, but it
is now progressing and diversifying at an amazing pace (for recent reviews, see e.g. Barrera and
# 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_14
625
Spectrometry
14
Summary
Mass spectrometry (MS) analyses of membrane proteins (MPs) have progressed
spectacularly over the past decade. Yet, the presence of detergents remains a source
of problems. In matrix-assisted laser desorption ionization (MALDI), only certain
detergents are acceptable, which are not necessarily those best tolerated by the
proteins under study. In electrospray ionization-mass spectrometry (ESI-MS) studies,
where MPs can be brought to the gas phase under their native oligomeric state and
conformation, a fine line has to be navigated between the Charybdis of retaining too
many detergent molecules, yielding unexploitable spectra, and the Scylla of using too
much collisional energy to strip away the detergent and denaturing the protein. The use
of amphipols (APols) as alternatives to detergents has been validated in these two
experimental configurations. MALDI-time-of-flight (TOF) experiments have been carried out using either A8-35 or non-ionic APols and have yielded mass determinations,
identification of posttranslational modifications and associated lipids, and sequence
data. In ESI-MS experiments, often combined with ion mobility (IM) measurements of
the collisional cross section of the protein, which yield information about its conformation, A8-35 has proven particularly convenient, protecting MPs against unfolding
better than the much used detergent dodecylmaltoside. Fast photochemical oxidation
has revealed details of the way the two surfactants interact with MPs that tally well with
the conclusions from molecular dynamics and NMR investigations. Whether APols can
be used to preserve the oligomeric state of MPs in the gas phase, however, is uncertain.
Finally, A8-35 has been used as a powerful tool to simplify whole proteome
investigations.
14.1 Introduction
The application of mass spectrometry (MS) to membrane proteins (MPs) is a relatively recent
development. As with most technologies, it has lagged behind application to soluble proteins, but it
is now progressing and diversifying at an amazing pace (for recent reviews, see e.g. Barrera and
# 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_14
625