A synthetic biosensor that mimics the properties of cell membranes and provides an electronic readout of activity could lead to a better understanding of cell biology, the development of new drugs and the creation of sensory organs on a chip capable of detecting chemicals, similar to how noses and tongues work.
January 18 in Synthetic biology Journal of the American Chemical Society.
The bioengineering feat described in the paper uses synthetic biology to repair the cell membrane and its embedded proteins, which are the watchdogs of cellular functions. The sensing platform allows an electronic readout when the protein is activated. The ability to test when and how a molecule interacts with proteins in the cell membrane could create a multitude of applications.
But incorporating membrane proteins into sensors was notoriously difficult until the study authors combined bioelectronic sensors with a new approach to protein synthesis.
“This technology really allows us to study these proteins in ways that would be incredibly difficult, if not impossible, with current technology,” said first author Zachary Munzer, a postdoctoral fellow in the lab of senior author Susan Daniel, the Fred H. Rhodes Professor and director of the School of Chemistry. and Robert Frederick Smith of Biomolecular Engineering at Cornell Engineering.
Proteins within cell membranes perform many important functions, including communicating with the environment, catalyzing chemical reactions, and moving compounds and ions across membranes. When a membrane protein receptor is activated, charged ions move through the membrane channel, triggering a function in the cell. For example, brain neurons or muscle cells fire when signals from nerves signal the opening of charged calcium ions.
The researchers created a biosensor that starts with a conductive polymer that is soft and easy to work with on top of a support that together act as an electrical circuit controlled by a computer. The layer of lipid (fat) molecules that forms the membrane rests on the polymer, and the proteins of interest are placed in the lipids.
In this proof of concept, the researchers created a cell-free platform that allowed them to synthesize a model protein directly in this artificial membrane. The system has built-in dual-read technology. Because the sensor components are transparent, researchers can use optical techniques, such as designing proteins that fluoresce when activated, allowing scientists to study the basics with a microscope and watch what happens to the protein itself during a cellular process. They can also record electronic activity to see how a protein functions through clever circuit design.
“This is really the first demonstration of using cell-free synthesis of transmembrane proteins in a biosensor,” Daniel said. “There’s no reason why we couldn’t express many different kinds of proteins into this common platform.”
Currently, researchers have used proteins grown and extracted from living cells for similar applications, but given this advance, users will not need to grow proteins in cells and then assemble and embed them into a membrane platform. Instead, they can synthesize them directly from DNA, the basic template for proteins.
“We can bypass the whole process of the cell being a protein-making factory,” Daniel said, “and make the proteins themselves in biomanufacturing.”
With such a system, a drug chemist interested in a particular disease-related protein can pass potentially therapeutic molecules through that protein to see how it reacts. Or a scientist who wants to create an environmental sensor could place a specific protein on the platform that is sensitive to chemicals or pollutants, such as those found in lake water.
“If you think about your nose or your tongue, every time you smell or taste something, the ion channels are triggered,” Munzer said. Now scientists can take the proteins that are activated when we smell and translate the results into this electronic system to sense things that cannot be detected with a chemical sensor.”
The new sensor opens up opportunities for pharmacologists to explore ways to create non-opioid pain relievers or drugs to treat Alzheimer’s or Parkinson’s disease that interact with cell membrane proteins.
Surajit Ghosh, a postdoctoral fellow in Daniel’s lab, is one of the authors. Neha Kamath, associate professor of biomedical engineering at Northwestern University, is the senior co-author of the paper.
The research was funded by the National Science Foundation, the Air Force Research Office, the American Heart Association, the National Institute of General Medical Sciences and the Defense Advanced Research Projects Agency.
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