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Simpler & smaller: a new synthetic nanofactory inspired by nature

Bacteria across our planet contain nanometer-sized factories that do many different things. Some make nutrients, others isolate toxic materials that could harm the bacteria. We have barely scratched the surface of their functional diversity.

But all share a common exterior, a shell made of expand iconprotein tiles, that we are learning how to manipulate in the lab. This will allow us to build factories of our own design, using these natural building blocks. Indeed, scientists see these structures as a source of new technologies. They are trying to repurpose them to do things they don’t in nature.

In a new study, the lab of Cheryl Kerfeld reports a new genetically engineered shell, based on natural structures and the principles of protein evolution. The new shell is simpler, made of only a single designed protein. It will be easier to work with and, perhaps, even evolve in the lab. The study is published in ACS Synthetic Biology.

Natural shells are made of up to three types of proteins. The most abundant is called BMC-H. Six BMC-H proteins come together to form a  hexagon shape to tile the wall.  

At some time in evolutionary history, some pairs of BMC-H proteins became joined together, in tandem. Three of these mergers, called BMC-T, join to also form a hexagon shape.

Evolution of BMC proteins into a nanofactory shell
Animation of how BMC-H evolves to BMC-T, and how these proteins contribute to form a nanofactory shell
MSU-DOE Plant Research Laboratory, 2019

“The two halves of a BMC-T protein can evolve separately while staying next to each other, because they are fused together. This evolution allows for diversity in the structures and functions of BMC-T shell proteins, something that we want to recreate by design in the lab,” says Bryan Ferlez, a postdoc in the Kerfeld lab.

Taking their cue from this natural evolution of shell proteins, the team created an artificial BMC-T protein, called BMC-H2, by fusing two BMC-H protein sequences together. The new design was successful.

“To our surprise, BMC-H2 proteins form shells on their own. They look like wiffle balls, with gaps in the shell,” says Sean McGuire a former undergraduate research student and technician in the Kerfeld lab.  This is because natural shells are icoshedral, meaning that they are made of expand iconhexamer and expand iconpentamers — think of a soccer ball. 

The new protein, BMC-H2 forms a new structure
Scientists copy what nature does to make a new, synthetic protein that forms a smaller, simpler shell.
MSU-DOE Plant Research Laboratory, 2019

Next, the team capped the gaps in the wiffle ball shell with BMC-P, the third type of shell protein that forms pentamers.

“The result is a shell, about 25 nanometers wide, made up of only two protein types: the new BMC-H2 and BMC-P,” Bryan says. “It is around half the size of the structure built with all three protein types.”

The next goal is to fit it with custom expand iconenzymes and fine tune it to enhance the chemical reactions within. The new ‘designer’ shell  could have uses in biofuel production, medicine, and industrial applications.


This work was primarily funded by the National Institutes of Health, National Institute of Allergy and Infectious Diseases, and the US Department of Energy, Office of Basic Energy Sciences.

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