Metallothioneins: new functional and structural insights.

In the past few years, tissue-specific mammalian metallothioneins (i. e. metallothionein-3 and metallothionein-4) have been discovered that possess distinct functional properties. Other recent developments include an insight into the role of the widely expressed mammalian metallothionein-1 and metallothionein-2 isoforms in zinc homeostasis and apoptosis. The three-dimensional structure of the evolutionary distant sea urchin Cd(7)-metallothionein A, which contains two metal-thiolate clusters, supports previous conclusions regarding the functional importance of this structural motif. Despite correlated efforts involving techniques of structural biochemistry and molecular biology, the primary function of metallothioneins remains enigmatic.