Chemistry Reference
In-Depth Information
lysozyme and ubiquitin, in microcrystals can be reduced to 60 ms by Cu-EDTA
doping without major degradation in the resolution of their
13
C CP-MAS spectra
[
181
]. They have further presented the paramagnetic relaxation-assisted condensed
data collection (PACC) experiment on
-amyloid fibrils and ubiquitin to obtain the
two-dimensional
13
C-
13
C and
13
C-
15
N SSNMR spectra in 1-2 d by reducing the
1
H
T
1
down to 50-100 ms with carefully adjusted paramagnetic doping [
182
]. This
sensitivity enhancement through shortening data acquisition time will make those
sophisticated and time-consuming multidimensional correlation experiments on
macrobiomolecules, such as membrane proteins become realistic.
b
3.7 Structure Determination Based on Chemical Shifts
The chemical shift of a nucleus directly reflects the electron density around it and
also reflects the influence of the local environment on it, including the nature of the
neighboring atoms and hydrogen-bonding, etc. Therefore, chemical shifts are
valuable parameters for protein structure determination. Very recently, three chem-
ical shift-based methods, Cheshire [
183
], CS-Rosetta [
184
], and CS23D [
185
] have
been reported to determine the native state structures of proteins in solution up to
130 residues and to a resolution of 2
˚
or better. These approaches have also been
successfully demonstrated to determine the native structures of GB1, GB3,
ubiquitin, and SH3 using SSNMR chemical shift data to a relatively high resolution
[
186
,
187
]. These methods may have the potential to determine the properties of
even bigger proteins, for example membrane proteins, to a higher resolution with
further improvement of the methods.
4 Perspective
Magic-angle spinning solid-state NMR has made tremendous progress, showing its
capability of determining membrane protein structure, ligand binding, and protein
dynamic conformation on a variety of time scales at atomic resolution. Further
developments may be threefold:
1. Sample preparation. New attempts might focus on developing new labeling
schemes to reduce further the spectral overlap and dipolar truncation,
expressing a sufficient amount of functioning membrane proteins using a cell-
free expression system, and a new approach to produce high ordered NMR
samples in membrane native environment.
2. New NMR methods which should be suitable for fully hydrated membrane
samples with better measurement accuracy and less dipolar truncation effects.
