Spatial Structure of Rabbit Liver Metallothionein-2 in Solution by NMR

Abstract

Sequence-specific assignments of the proton spin systems of (Cd₇) rabbit liver metallothionein-2 were obtained with homonuclear two-dimensional nuclear magnetic resonance techniques. On the basis of the NMR data the amino acid sequence had to be modified in six positions, and it was found that the protein consists of 62 rather than 61 residues. Through-bond connectivities between the metals and sequentially assigned cysteine residues were obtained with two-dimensional heteronuclear ¹H-¹¹³Cd correlated spectroscopy. This information, and distance constraints obtained from nuclear Overhauser enhancement spectra were used as input for distance geometry calculations of the spatial polypeptide fold. The polypeptide chain forms two domains which enclose a three-metal cluster and a four-metal cluster, respectively. The metal coordination within the clusters is markedly different from that of (Cd₅, Zn₂)-MT-2 from rat liver as determined by X-ray crystallography (Furey, et al., 1986) i.e. in the two structures different metal-cysteine combinations prevail for 5 of the 12 connectivities in the three-metal cluster and for 14 of the 16 connectivities in the four-metal cluster.