Oxidative dimerization in metallothionein is a result of intermolecular disulphide bonds between cysteines in the α-domain

Upon storage under aerobic conditions metallothioneins (MTs) form a new species, which is characterized by a molecular mass approximately twice the size of monomeric MT and shifted ^113/111Cd- and ¹H-NMR resonances. The investigation of this oxidative dimerization process by NMR spectroscopy allowed us to structurally characterize this MT species that has been described to occur in vivo and might be synthesized under conditions of oxidative stress. The oxidative dimer was characterized by the formation of an intermolecular cysteine disulphide bond involving the α-domain, and a detailed analysis of chemical shift changes and intermolecular nuclear Overhauser effects points towards a disulphide bond involving Cys³⁶. In contrast to the metal-bridged (non-oxidative) dimerization, the metalcysteine cluster structures in both MT domains remain intact and no conformational exchange or metal - metal exchange was observed. Also in contrast to the many recently reported oxidative processes which involve the β-domain cysteine groups and result in the increased dynamics of the bound metal ions in this N-terminal domain, we found no evidence for any increased dynamics in the α-domain metals following this oxidation. Therefore these findings provide additional corroboration that metal binding in the C-terminal α-domain is rather tight, even under conditions of a changing cellular oxidation potential, compared with the more labile/dynamic nature of the metals in the N-terminal β-domain cluster under similar conditions.