Yeast, bacteria and mammalian cells are often harnessed to act as small factories that produce drugs, biofuels and other products. Megan McClean, an associate research scholar in Princeton’s Lewis-Sigler Institute for Integrative Genomics, has developed a system for real-time control of the amount of protein made by yeast in these biological factories.
     McClean’s system uses blue light to turn on protein production in these cells, which are housed in large containers known as bioreactors. The system contains detectors that sense current protein levels and either ramp up or down the production of the protein.
     The system relies on a technology known as optogenetics, which involves using a beam of light to turn on or off specific genes. Optogenetics takes advantage of the fact that certain light-sensitive proteins will change shape when hit by blue light. When the protein changes shape, it becomes able to bind to a second protein that then activates the reading of the DNA that codes for the creation of a desired protein product.
     McClean has attached this optogenetic “on/off” switch to a gene for a desired protein in yeast cells growing in a bioreactor, and shining blue light into the bioreactor causes a surge in production of this protein. By including a gene for a fluorescent tag, McClean can measure the emission of fluorescent light to quantify the amount of protein produced.
     McClean has built this protein production control mechanism into a robotic bioreactor system that a researcher can use to produce a preset amount of protein in yeast. The researcher enters the desired quantity into a computer connected to a bioreactor. Then the blue light is turned on, activating the reading of the DNA code and the production of the protein. At periodic intervals, small amounts of cells are drawn into a detector that quantifies protein concentration by measuring the amount of fluorescence being emitted. When the fluorescence detector indicates that the preset amount of protein has been reached, the blue light turns off and production of the drug shuts down.
     The system can be used to preset levels of production or to create proteins on a schedule, McClean said. “I tell the computer how much protein production I need, and when I need it, and the computer software turns on and off the blue light,” McClean said. She developed the system with the help of Research Specialists Justin Melendez and Michael Patel, former Research Specialist Benjamin Oakes, and Associate Research Scholar Marcus Noyes in the Lewis-Sigler Institute.
     McClean hopes that the system can be used by pharmaceutical companies to produce new products, as well as for basic research. “For example, researchers could overexpress or underexpress levels of a specific protein and then study the downstream effects,” she said. Another possible use, she said, is the optimization of ethanol production for biofuels.