Anal. Chem. 2005, 77, 5036-5040
Combination Detergent/MALDI Matrix: Functional
Cleavable Detergents for Mass Spectrometry
Jeremy L. Norris, Ned A. Porter, and Richard M. Caprioli*
Department of Chemistry and Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232-8575
that the solubility problems can be overcome.2,3,8,9 Reagents that
provide for the extraction and solubilization of hydrophobic
proteins, while allowing subsequent analysis of the isolated protein
using mass spectrometry, will be of great value.
This study reports the synthesis of the first functional
cleavable detergent designed specifically for applications
in mass spectrometry. Upon cleavage, two inert com-
pounds and the MALDI matrix are formed, eliminating
sources of potential interference originating from tradi-
tional cleavable detergents. Analysis of peptides demon-
strates that MALDI matrix generated in situ results in
MALDI spectra equivalent to those prepared using estab-
lished protocols. Analysis of the membrane protein dia-
cylglycerol kinase was accomplished using the combina-
tion detergent/MALDI matrix. Applications of the functional
cleavable detergents to the profiling of whole cell lysates
results in increased signal-to-noise ratios of many ions and
the detection of additional proteins previously not ob-
served.
Cleavable detergents are reagents that have properties similar
in all ways to conventional detergents.1
0-12
However, cleavable
detergents have the added benefit that when they are no longer
necessary, they can be selectively degraded to yield products that
have reduced or no surface activity. These innovative reagents
have found a number of applications in industrial processes and
chemical syntheses because they can be easily and completely
removed when they are no longer needed. The development of
cleavable detergents is an established field that has experienced
significant resurgence in the past few years. The reason for such
renewed interest is due in large part to novel applications of these
reagents to problems in the analysis of biologically significant
molecules. Various types of cleavable detergents have been
The use of detergents to enhance the solubility of otherwise
insoluble compounds has been part of general biochemical
protocols for decades. Detergents provide a means by which these
molecules can be extracted and isolated from other components
synthesized that are suitable for the analysis of proteins using
two-dimensional gel electrophoresis.1
3-17
These techniques were
not successfully reduced to practice until the recent introduction
15-17
of an acid-labile surfactant
based on a structure first synthe-
1
of the cell for further study. Unfortunately, many of the detergents
sized by Jaeger et al.18 These compounds allow two-dimensional
gel analyses of a quality comparable to that of traditional SDS-
PAGE analyses while retaining the ability to identify the separated
proteins using chromatography and mass spectrometry. Acid-
cleavable detergents are also useful for mass spectrometric
analysis of intact membrane proteins and analyses requiring the
direct profiling of cells and tissue with matrix-assisted laser
used today also hinder analytical characterization of biomolecules
because they aggregate to form noncovalent, nonspecific com-
plexes with the desired analyte. One specific example of this
phenomenon is the suppression of ions that occurs during mass
spectrometry of proteins that are detergent solubilized. The
difficulties associated with detergents in mass spectrometry are
well documented and continue to impede efforts to develop
analytical techniques to study hydrophobic proteins using mass
(
8) Ghaim, J. B.; Tsatsos, P. H.; Katsonouri, A.; Mitchell, D. M.; Salcedo-
Hernandez, R.; Gennis, R. B. Biochim. Biophys. Acta 1997, 1330, 113-
120.
2
-7
spectrometry.
There have been a number of studies that
suggest there are no intrinsic properties of membrane proteins
that would prohibit analysis using mass spectrometry provided
(9) Cadene, M.; Chait, B. T. Anal. Chem. 2000, 72, 5655-5658.
(10) Hellberg, P.-E.; Bergstrm, K.; Holmberg, K. J. Surfactants, Deterg. 2000,
3
, 81-91.
*
To whom correspondence should be addressed: (e-mail) R.Caprioli@
(11) Holmberg, K. In Novel surfactants: preparation, applications, and biodegrad-
ability; Holmberg, K., Ed.; Marcel Dekker: New York, 1998; Vol. 74, pp
333-359.
(12) Jaeger, D. A. Supramol. Chem. 1995, 5, 27-30.
(13) Epstein, W. W.; Jones, D. S.; Bruenger, E.; Rilling, H. C. Anal. Biochem.
1982, 21, 304-312.
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5036 Analytical Chemistry, Vol. 77, No. 15, August 1, 2005
10.1021/ac050460g CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/16/2005