Biomedical Engineering Reference
In-Depth Information
Figure 2.5
Benefit of non-uniform sampling (NUS) compared to uniform acquisition
and linear prediction. (A) Representative strips from the NCA spectrum
of alternately
13
C-labelled protein GB1. The four strips at the left
represent experiments with the same total measuring time (512 total
scans). Strip 5 was recorded with 256 linear increments and eight scans
per increment (2048 total scans), requiring a 4-fold longer experiment.
For panel A2, the first 64 linear increments were extended with linear
prediction using an order parameter of 30. Panels A3 and A4 were
obtained with random sampling (64 points) and SPS (64 points),
respectively. (B, C) Plots of the S/N values of (B) all and (C) only small
peaks. The S/N values of the selected peaks obtained with procedures A1-
A4 are plotted against the A5 S/N. Adapted from ref. 70.
unstructured regions. In contrast, the NCA signals are clearly visible for all
region of the protein.
In addition, a 3D version of the
13
C
a
-detected experiment, CANCA, which
would avoid signal overlap in larger proteins, has been developed
(Figure 2.7).
51
The C
a
direct-detected 3D CANCA experiment provides a
robust way to establish complete main-chain resonance assignment with
simultaneous use of both C
a
and N sequential connectivities. The 3D CANCA
experiment correlates a given alpha carbon (C
a
i
) both with its attached
nitrogen (N
i
) and the nitrogen of the following residue (N
i+1
). In another
dimension, this a-carbon is correlated with the C
a
of both previous (C
a
i21
)and
following (C
a
i+1
) residues. This enables elongation of the chain of assigned
residues simply by navigating along both dimensions using the so-called
