Scientists in Japan have used an artificially designed protein to create a cadmium chloride nanocrystal, the smallest crystal reported so far, consisting of only 19 atoms, sandwiched between two copies of the protein.
It is known that proteins use the process of biomineralization, in the natural world, to incorporate metallic elements into tissues, creating such diverse materials as seashells, teeth, and bones. What is still unclear is the way proteins actually do this.
The goal of the groups’ was to design novel proteins, which do not exist in nature, that could be put to a variety of uses.
Modifying Pizza Proteins
With its high degree of symmetry, a protein like Pizza6 does not exist naturally. But since such proteins can be created artificially, they are attractive scaffolds for the creation of new hybrid biomaterials suited to a variety of purposes such as drug packaging for delivery to cells, or even bioremediation of hazardous metals in the environment.
This new research modified the Pizza protein by introducing a metal-binding site. Explained first author Arnout Voet, who designed and built the proteins:
“Our initial impetus was to design metal-binding sites to control the self-assembly of our designed symmetrical proteins. We used computational methods to find a rational way to incorporate a metal-binding site into the Pizza protein we had previously designed, based on the idea that this could allow us to control protein assembly easily. We believe that this would give us a new tool for building novel proteins from the ground up by using very cheap metal reagents.”
When the proteins were modified to have a metal-binding site, then placed in a solution of cadmium chloride, the researchers found that trimers of the protein would spontaneously bind together.
Using RIKEN’s Spring-8 synchrotron facility in Harima and other facilities, they analyzed the structure at the atomic level and discovered that the atoms of cadmium and chloride had formed a tiny lattice, a crystal structure, sandwiched between two “pizzas.”
Corresponding author Kam Zhang, who led the RIKEN team, said:
“We were very excited to see the formation of the crystal, as it provides insights into the process of biomineralization—the process through which nature incorporates metallic elements into tissues to form structures such as seashells, teeth, and bones.
Our results indicate the feasibility of using rationally-designed symmetrical proteins to biomineralize nanocrystals. Achieving this could allow us to make a wide range of nano-devices such as biopharmaceuticals, biosensors, light-driven switches, and synthetic enzymes from the bottom up.”