Metallothionein (MT) has provided nature with a small molecule which e
xhibits multiple facets. The distinct arrangement of cysteine residues
which occurs within the two domains of MT confers predisposed metal s
pecificity upon each domain. Furthermore, subtle changes in primary se
quence may be built onto the metal cluster scaffold. These not only be
stow 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-bindi
ng molecules specific for the metal ion of choice. Already, using natu
re as a blueprint, a semi-specific cadmium-binding molecule has been c
onstructed 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 l
ocated on the external face of MT-III may facilitate the design of sma
ll synthetic molecules which mimick the biological activity of MT-III
and prevent the distressing effects of memory and speech loss associat
ed with Alzheimer's disease. Memories of metallothionein may yet be so
mething worth remembering!