Studying protein conformers in solution using ESI MS and chemometric
approach.
Electrospray ionization (ESI) is a soft
ionization technique that produces multiply charged ions of biological
molecules. Protein ion charge state
distributions in ESI mass spectrometry (MS) provide information on protein
dynamics, as it contains contributions from all protein conformers present in
solution. Such ionic contributions often overlap, limiting the amount of useful
information that can be extracted from the spectra. This difficulty can be
overcome by using factor analysis, which allows spectral deconvolution
to be carried out and information on individual protein conformers to be
extracted. Experiments were
carried out by acquiring a series of spectra over a range of near-native and
denaturing conditions to ensure significant changes in the conformers’
populations. The total number of protein conformers sampled in the course of
the experiments was then determined by subjecting the set of spectra to singular
value decomposition. Ionic contributions of each conformer to the total signal
are then determined using a supervised minimization routine. By monitoring acid
and alcohol induced equilibrium intermediates of well-characterized model
proteins: chymotrypsin inhibitor 2 (two states),
ubiquitin (three states) and apo-myoglobin (four
states), we can demonstrate that factor
analysis correctly predicts the total number of conformations of the three
model proteins under a variety of conditions.
Evolution of each conformer’s ionic contribution from minimization
routine is in agreement with the expected behavior of these species, as
documented based on the results of earlier studies that used a variety of
biophysical techniques. For a detailed
description look please look at the journal below.
Anal. Chem. 2003,
75, 4139-4147.
The above chemometric approach can also be used
to study the solvent accessible surface areas of proteins, and so far the
method is sensitive enough to measure even minute protein transition states.
Also studying:
Charge distribution and the choice of
electrospray solvent
Natively unstructured proteins using
FT-ESI-MS
ESI-MS of lipids
LC-MS of taxanes