Preparation and reactivity of a tetranuclear Fe(II) core in the metallothionein α-domain.

Metallothioneins (MTs) are small cysteine-rich proteins which exhibit high affinities for various metal ions and play roles in storage of essential metals and detoxification of toxic metals. Studies on the redox properties of MTs have been quite limited. Recently, we focused on the α-domain of MT (MTα) as a protein matrix and incorporated a tetranuclear metal cluster as a reductant. UV–visible, CD and MS data indicate the formation of the stable tetranuclear metal–cysteine cluster in the MTα matrix with FeII4–MTα and CoII4–MTα species existing in water. Furthermore, the FeII4–MTα species was found to promote the reduction of met-myoglobin and azobenzene derivatives under mild conditions. Particularly, the stoichiometric reduction of methyl red with FeII4–MTα (1:1) was found to proceed with a conversion of 98% over a period of 6h at 25°C. This indicates that all of the four Fe(II) cores contribute to the reduction. In this paper, we describe the preparation and reactivity of the tetranuclear iron cluster in the protein matrix.