Plant Protein Powers Red Light-Activated Switch for Animal Cells

An optogenetic switch activated by red and far-red light has been designed and tested in animal cells. The light-activated switch, which does not require the addition of sensing molecules from outside the cells, could be used to turn genes on and off in gene therapies; to turn off gene expression in future cancer therapies; and to help track and understand gene function in specific locations in the human body.

Researchers from the University of California San Diego, Quinnipiac University, and the University of Iowa devised a way to enable animal cells to transfer enough electrons from their energy supply to enzymes that could produce the light-sensitive molecules needed for the optogenetic switch. They used bacterial and plant ferredoxin (Fd), an iron and sulfur protein that facilitates electron transfer, to enhance production of chromophores in mammalian cells. Ferredoxin-NADP⁺ reductase (FNR) was used to express the bacterial and plant Fd.

UC San Diego postdoctoral researcher Phillip Kyriakakis demonstrates the desktop system powered by the optogenetic switch. Courtesy of University of California San Diego.

Although Fd exists in animal cells, it exists in a form that is not compatible with plant and bacteria Fd. FNR was used to adapt the bacterial and plant Fd to the animal cells.

Researchers optimized the production system for bacterial Fd and combined it with a tissue-penetrating red-/far-red-sensing phytochrome B (phyB) optogenetic gene switch in animal cells. The light-sensitive molecules were placed in the cell’s mitochondria. Researchers characterized this system in several mammalian cell lines using red and far-red light.

Bioengineers built and programmed a small, compact tabletop device to activate the switch with red and far-red light. The tool allows researchers to control the duration that the light shines, down to the millisecond. It also allows them to target specific locations.

The desktop system consists of a box and a touch-screen interface for tablets. Courtesy of University of California San Diego.

The team found that the light-switchable gene system remained active for several hours upon illumination, even with a short light pulse, and that it required very small amounts of light for maximal activation.

“Being able to control genes deep in the body in a specific location and at a specific time, without adding external elements, is a goal our community has long sought,” said Todd Coleman, a professor of bioengineering at UC San Diego. “We are controlling genes with the most desirable wavelengths of light.”

Red light is a safe option to activate genetic switches because it easily passes through the human body.

The research team patented the use of Fd's and FNR to target the enzymes needed to make light-activated molecules. The technology is available for licensing.

The team believes that boosting chromophore production by matching metabolic pathways with specific Fd systems could enable the use of phyB optogenetic tools and could have broader implications for optimizing synthetic metabolic pathways.

The research was published in ACS Synthetic Biology (doi:10.1021/acssynbio.7b00413).