Biomedical Engineering Reference
In-Depth Information
Although
13
C-detection methods have been established as the primary
alternative to
1
H-detected NMR,
15
N-detection experiments have also been
proposed recently,
40,41
and also much earlier.
42
Recently it was also shown that
the anisotropic component (CSA) of
15
N chemical shielding can be more
accurately estimated by nitrogen-detected NMR experiments in D
2
O.
40
The
obtained
15
N chemical shielding tensors contain useful structural information,
and their knowledge is essential for the accurate analysis of protein backbone
dynamics.
Here we provide an overview of the current state of low-c detection
experiments and provide an outlook for future developments.
2.2 Relaxation Properties of Low-c Nuclei
Figure 2.1 summarises estimates of the transverse relaxation rates of low-c
nuclei as a function of the overall correlation time at two different magnetic
fields (11.7 T and 18.8 T corresponding to proton frequency of 500 and 800
MHz, respectively) for (A) a uniformly
15
N,
13
C-labelled and (B) a uniformly
Figure 2.1
Transverse relaxation rates of low-c nuclei as a function of the overall
correlation time at two different magnetic fields (11.7 T, corresponding to
proton frequency of 500 MHz, solid line, and 18.8 T: 800 MHz, dashed
line). (A) is for a uniformly
15
N
13
C-labelled and (B) is for a uniformly
2
H
15
N
13
C-labelled protein. The dipole-dipole interactions with directly
bonded nuclei as well as nuclei within defined distances were used to
mimic the typical proton density in a protein. The distance cut-off criteria
were, ,4.5
˚
for
1
H-
1
H pairs, ,3.3
˚
for
1
H-
13
C pairs, and ,2.1
˚
for
1
H-
15
N pairs. Typical distances in an a-helix region were used for the
estimates. Chemical shift anisotropies were also included for the
calculation (Dd
15
N
H
: 2160 ppm, Dd
13
C
a
: 2.2 ppm, Dd
13
C9: 170 ppm).
Abbreviations are C
a
H
: proton-attached
13
C
a
,C
a
D
: deuterium-attached
13
C
a
,N
H
(Dec):
15
N
H
15
N
H
with
proton
decoupling,
N
D
(Dec):
with
15
N
H
deuterium
and
proton
decoupling,
N
H
(TR):
TROSY
line
of
15
N decoupling,
without proton decoupling, H
N
: amide proton with
15
N decoupling.
H
N
(TR): TROSY line of amide proton without
