Everything started with an oyster, Crassostrea rhizphorae. We were amazed by how this tropical oyster survives in environments highly polluted by heavy metals! Soon, we learned that one of its first line of defenses against metals is a protein called metallothionein, or just MT.
We isolated its MT gene, produced and studied oyster MT protein in vitro. By doing so, we showed that MT binds metals tightly and, under certain conditions, releases those metals back. The graph below illustrates the pattern we observed, where the more metal we give, more metal is bound by oyster MT, until the protein is fully loaded. If certain conditions are applied, we can see metal being released by MT along the time. We tested this for both cadmium and zinc.
A protein able to catch and release metals in a controlled fashion like that would have great applications in the metal industries. One could use it to remove metals from industrial wastes, cleaning it and at the same time recovering those metals for recycling. Following the same logic, one could use it to concentrate and recover metals during challenging mining. Nevertheless, we were still not satisfied with it and, with the advent of DNA synthesis technology, we thought we could do better. Therefore, based on the natural oyster MT gene, we developed a new synthetic MT, named MTαβ4, with an increased number of metal-binding domains (named α and β, as shown below). MTαβ4 was designed to bind four times more metals than the natural oyster MT. By means of similar in vitro studies, we showed, using nickel as example, that MTαβ4 is functional and binds and release metals, as expected!
