Memories of metallothionein.

Metallothionein (MT) has provided nature with a small molecule which exhibits multiple facets. The distinct arrangement of cysteine residues which occurs within the two domains of MT confers predisposed metal specificity upon each domain. Furthermore, subtle changes in primary sequence may be built onto the metal cluster scaffold. These not only bestow immunodistinction but may also potentially allow specific members of this family such as MT-III to fulfill unique biological roles. An understanding of how the structures of MT molecules predetermine their biochemical characteristics may allow the design of novel metal-binding molecules specific for the metal ion of choice. Already, using nature as a blueprint, a semi-specific cadmium-binding molecule has been constructed from a polymer of mammalian C-terminal domains. This novel protein has been used to protect tobacco plants from cadmium toxicity. In addition, modeling of biologically active determinants which are located on the external face of MT-III may facilitate the design of small synthetic molecules which mimic the biological activity of MT-III and prevent the distressing effects of memory and speech loss associated with Alzheimer's disease. Memories of metallothionein may yet be something worth remembering!