A new way to hoard resources in nano-sized factories targeted for biotech
Cheryl Kerfeld's laboratory at Michigan State University has created a nanometric synthetic plant based on natural bacteria. This research could one day lead to new medical, industrial or bioenergy applications.
The new study is published in Metabolic Engineering.
Natural nanofacteria are found in bacteria all over the world. Some produce nutrients. Others sequester toxic materials that would otherwise make the bacteria sick or even deadly.
But all plants share a common exterior, a shell made of protein tiles. Scientists want to design new plants, based on those found naturally in bacteria, for use in biotechnology.
One way to direct useful enzymes to these plants is to physically attach them to the tip of the tail of the proteins that make up the plant shell. But there is a trap.
The ends, or termini, of most shell protein tiles face outside a factory. Thus, any molecule fused to the ends of the proteins will be found on the outer surface and not inside. This is a problem if the goal is to maintain one or more enzymes inside a plant separate from the rest of the cell.
"To send proteins inside the plant, we needed a new type of building block that would still be assembled in shell," says Bryan Ferlez, a postdoctoral researcher at the Kerfeld laboratory. "We wanted to redesign a shell protein so that its ends would face inwards. The final result is that the cargo bound to this shell protein would also be found inside the shell."
Credit: Michigan State University
In the new study, scientists take the most abundant shell protein, called BMC-H, and turn it "upside down" by a technique called circular permutation.
They mix the segments of the amino acid sequence and glue the original ends together. They then introduce new terminuses on the inner side of the protein. The result is a new synthetic shell protein that looks almost identical to its natural counterpart. Except now, the two new ends face inside the shell.
The new structure is a building element that can be used for the construction of factory hulls. Scientists have been able to produce factory shells with the new protein. Their size and appearance are similar to those of the original shells.
The new structure can incorporate molecules inside the shell. The team tested the concept by fusing a fluorescent cargo protein with the new BMC-H protein. Microscopy and biochemical tests show the cargo inside the hull.
Scientists can control the quantity of imported goods in the new structure.
"By making more or less the new BMC-H protein with a fluorescent protein fused at its end, we were also able to control the amount of cargo that gets incorporated into the shell," said Mr. Ferlez.
Then, Ferlez wants to target "useful" molecules in a synthetic plant manufactured with the new shell protein.
"We can start building metabolic pathways, or assembly lines, and define the quantities and location of enzymes in these nano-plants. One day, we could use this system to improve the production of rubber, biofuels and other commodities," explained Mr. Ferlez.
