Comparison of the solution conformations of human [Zn7]-metallothionein-2 and [Cd7]-metallothionein-2 using nuclear magnetic resonance spectroscopy.

The solution structure of native human Zn7]-metallothionein-2 has been compared with the previously determined structure of human Cd7]-metallothionein-2. The comparison was based on complete sequence-specific 1H nuclear magnetic resonance assignments for human Zn7]-metallothionein-2 obtained using the sequential assignment method. The secondary structure was found to be very similar in the Zn7]- and Cd7]- forms of the protein. Only seven amide protons in Zn7]- metallothionein-2 were found to have exchange rates lower than approximately 0.2 min-1 at pH 7.0 and 10 degrees C, which corresponds closely to the results of amide proton exchange studies with the Cd7]- form of the protein. Finally, the 1H-1H distance constraints determined from nuclear Overhauser enhancement spectroscopy for human Zn7]-metallothionein-2 were checked for compatibility with the Cd7]-metallothionein-2 structure. Overall, although no direct method is available for identifying the metal-polypeptide co-ordinative bonds in the Zn(2+)-containing protein, these measurements provided several independent lines of evidence showing that the Zn7]- and Cd7]- forms of human metallothionein-2 have the same molecular architecture.