Determination of the solution three dimensional structure of chemically-synthesized native ¹¹³Cd₃S₉ domain of Lobster Metallothionein by NMR Spectroscopy

Amalia Muņoz^*, F. Holger Forsterling, C. Frank Shaw III⁺ and David H. Petering

Structure Determination

Tetrahedral geometry coordination of the cluster was fixed according to metal complexes with Cd-S bonds of 2.54 A using constants of 500 kcal/mol A² and for the angles S-Cd-S and Cd-S-Cd and C^b-S-Cd of 250 kcal/mol A². Simulated annealing protocol was used to obtain the final structures with minimal energies.

Analysis of the secondary structure indicates that as in the cae of other mammalian or crustacean metallothioneins, the 3D-structure is driven only by the metal-cysteine coordination, thus only a single element of secondary structure was observed, an helix 3-10 between residues 44-47. This element seems to be always present in the C-terminal domain of the holoprotein structures, which may indicate a structural-functional motive within the protein.

Figures 7 and 8. An anssemble of the lower 18 energies structures and the ribbon representation showing the helix 3-10 motive are shown in the next two figures. In these images is also clear the boat conformation of the beta-cluster in metalloclusters of metallothioneins. of 3 mM Cd₃ß_C in 5 mM d₁₁-Tris-HCl at pH 7.5.