Mn,Cd-metallothionein-2: A room temperature magnetic protein

Naturally occurring metallothionein (MT) is a metal binding protein, which binds to seven Zn²⁺ through 20 conserved cysteines and forms two metal binding clusters with a Zinc-Blende structure. We demonstrate that the MT, when substituting the Zn²⁺ ions by Mn²⁺ and Cd ²⁺, exhibits magnetic hysteresis loop observable by SQUID from 10 to 330 K. The magnetic moment may have originated from the bridging effect of the sulfur atoms between the metal ions that leads to the alignment of the electron spins of the Mn²⁺ ions inside the clusters. The protein backbone may restrain the net spin moment of Mn²⁺ ions from thermal fluctuation. The modified magnetic-metallothionein is a novel approach to creating molecular magnets with operating temperatures up to 330 K.