Biomedical Engineering Reference
In-Depth Information
Figure
2.9
The CAN experiment optimized for uniformly
2
H
15
N
13
C-labelled
samples. (A) Illustration of the coherences correlated in the CAN
experiment with a schematic representation of the 2D CAN spectrum.
The nuclei involved in this experiment are coloured in red. Arrows
indicate the magnetic transfer pathways in the CAN experiment. (B and
C) Comparison of (B) CAN and (C) NCA-DIPAP spectra recorded with
the same experimental time. Both spectra are shown at the same scale in
Hz for the direct dimension and the same number of points was recorded
for the indirect dimension. The Phe52 intra-residual cross peak is
enlarged in the inset panels and the corresponding 1D slices along the
direct dimension are shown at the top of the 2D spectrum as well as in
the enlarged panels. Details of the experiment can be found in the
original literature. Adapted from ref. 41.
have superior resolution and signal overlap is much less severe than in the
proton-detected experiments [Figure 2.10(C)]. It is worth noting that 13 out of
14 Pro C
d
-N correlations were observed and are placed in a dashed frame in
Figure 2.10(A). All but one of the Pro C
d
-N correlations can be associated with
the corresponding C
a
-N cross-peaks with carbon chemical shifts around 61-67
ppm. Three of them have additional signals in carbon chemical shifts below 60
ppm, which correspond to sequential correlations. This indicates that most of the
intra-residual correlations are observed in this spectrum, while sequential
correlations are barely above the noise level. It is clear that further improvements
need to be introduced at the hardware level as well as in data acquisition and
processing to enable routine use of this experiment for very large proteins.
An experiment for detecting
13
C9-
15
N correlations, CON, was designed with
a similar pulse scheme as CAN. While the
13
C9 transverse relaxation is faster
compared to
13
C
a
in higher molecular weight proteins and in high magnetic
fields, it may nevertheless be beneficial to utilise the efficient coherence transfer
pathway. In addition, the 'out-and-stay' type transfer used in the CON
experiment shortens the C9 transverse period to 33 ms compared to 66 ms used
