UWM Chemistry NMR facility
bar.gif

UWM Logo

Lobster Metallothionein 113Cd3-b Domain Solvent Atom Exposure Patterns Studied by NMR Spectroscopy:
Impact on Metal-Thiolate Cluster Reactivity

bar.gif
bar.gif

Comparison to Crab-MT1

The overall backbone fold in the isolated lobster Cd3 b domains resembles the ones also found in Crab-MT. However, a closer comparison reveals that the HN chemical shifts of Cys5 and E10 differ significantly for lobster-MT when compared to Crab-MT (Figure 7, left) [2] and the holo protein of lobster-MT [3 ]. Since the difference is common to both the isolated domain Cd3-bN and the holo protein of lobster-MT, it is most likely related to a structural change related to a difference in the sequence. It is interesting to note that in the case of Cd3-bN a strong cross peak due to a NH...S hydrogen bond is observed between those two residues. Furthermore, E10 is substituted by V10 in the case of Crab-MT, giving rise to the speculation that the nature of residue 10 influences the strength of the hydrogen bond (E10)NH...S g(C5) observed in MT-bN
Upon closer inspection of the two structures it turns out that the backbone f angles for Cys5 differ, resulting in the NH bond of that residue being oriented very differently. In the case of lobster-bN the NH bond of Cys5 is directed toward the general direction of the Glu10 residue. In the average NMR structure the sidechain of Glu10 does not get near Cys5. However the atoms of the E10 sidechain are not very well defined and conformations with the sidechain in the proximity of C5 also fulfill the NMR restraints. Indeed, molecular dynamics calculations suggest that a (C5)NH... Oe(E10) hydrogen bond might exist in Cd3-bN. An equivalent H-bond is not possible in the case of Crab-MT.
The shift difference of C27 is unique to the isolated domain, whereas the change in S50 is most likely due to a wrong assignment in the case of the holo protein of lobster-MT [3]. bar.gif
Figure 7: Left: HN proton chemical shift difference between the isolated MT-b domains and the holo proteins of Lobster- and Crab-MT. Residues exhibiting major differences are indicated. Right: Ball and stick display of residues 5 and 10 in the NMR structures of Cd3bN and Crab-MT[2]. The conformation of the E10 sidechain in Cd3bN suggested by molecular dynamics calculations is shown as dashed orange line.
bar.gif
bar.gif
To Top of This Page NMR Home back to NMR lab on line posters To Poster-On-Line
Converted to HTML by F. Holger Försterling March 2001