Protein Structure and Dynamics by NMR in Solution
III
y
Fig. 7.7. Anisotropic rotational diffusion tensor of cytochrome c,. The backbone of cytochrome c,
(NMR structure) is shown in a ribbon representation, helices are given by cylinders. The tensor is
characterized by the orientation of its three principal axis as shown. Its component values have been
calculated to Dxx=1.829, Dyy = 1.566 and Dzz = lAOS from the relaxation data
(Fig. 7.7). We have again used robust statistical tests to analyze the significance of
the improved fit and shown that the fully anisotropic tensor is justified in this
case.
4.2.2
Comparison of Structural and Dynamic Information
The spatial order of the individual NH vectors present in the NMR ensemble has
been compared to motional parameters fitted to the model-free approach using
the asymmetric anisotropic diffusion tensor. Although the protein is relatively
compact, giving rise to high order parameters and low internal flexibility
(Fig. 7.8), certain regions of the molecule appear to exhibit coincident dynamic
behavior and low structural order. In particular the loop (A101-G103), situated
between the heme-methionine binding motif and the C-terminal helix. This tripeptide may be important for electrostatic interactions with electron transfer
partners, as K102 makes up part of the positively charged interaction surface
common to all cytochrome c and C2 proteins (Tiede et al. 1993), a region which
III
y
Fig. 7.7. Anisotropic rotational diffusion tensor of cytochrome c,. The backbone of cytochrome c,
(NMR structure) is shown in a ribbon representation, helices are given by cylinders. The tensor is
characterized by the orientation of its three principal axis as shown. Its component values have been
calculated to Dxx=1.829, Dyy = 1.566 and Dzz = lAOS from the relaxation data
(Fig. 7.7). We have again used robust statistical tests to analyze the significance of
the improved fit and shown that the fully anisotropic tensor is justified in this
case.
4.2.2
Comparison of Structural and Dynamic Information
The spatial order of the individual NH vectors present in the NMR ensemble has
been compared to motional parameters fitted to the model-free approach using
the asymmetric anisotropic diffusion tensor. Although the protein is relatively
compact, giving rise to high order parameters and low internal flexibility
(Fig. 7.8), certain regions of the molecule appear to exhibit coincident dynamic
behavior and low structural order. In particular the loop (A101-G103), situated
between the heme-methionine binding motif and the C-terminal helix. This tripeptide may be important for electrostatic interactions with electron transfer
partners, as K102 makes up part of the positively charged interaction surface
common to all cytochrome c and C2 proteins (Tiede et al. 1993), a region which