Metallothioneins: new functional and structural insights

In the past few years, tissue-specific mammalian metallothioneins (i.e, met allothionein-3 and metallothionein-4) have been discovered that possess dis tinct functional properties. Other recent developments include an insight i nto the role of the widely expressed mammalian metallothionein-l and metall othionein-2 isoforms in zinc homeostasis and apoptosis. The three-dimension al 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 corre lated efforts involving techniques of structural biochemistry and molecular biology, the primary function of metallothioneins remains enigmatic.