Reprogramming Proteins
A Genetic Approach to Functional Materials
We are interested in creating “smart” materials that sense their environment and respond with changes in their mechanical properties. The ability to sense and respond to environmental changes is a hallmark of even the simplest living systems, which use proteins to sense the environment and perform mechanical work. While many engineered materials mimic or directly incorporate elements of proteins for their mechanical properties, relatively few materials incorporate natural proteins as sensing elements. We are creating genetically engineered frameworks that enable rapid combinatorial synthesis of proteins that reversibly self-assemble in the presence of various molecules or ions.
By using genetically encoded polymers, we have absolute control over the length and composition of every molecule in the sample. This control allows us to precisely tune the properties of the materials and to 
correlate chemical-scale behavior (such as a binding constant) with mechanical behavior (such as the ability to form a gel). In addition to providing a high-level of control over the materials properties, this ability to correlate microscopic and macroscopic behavior allows us to express materials engineering problems in chemical terms. Ultimately, we would like to predict mechanical properties from the dilute-solution behavior of the protein components. Realizing this goal would allow us to use directed evolution to select for proteins with a desired property, such as an altered ligand sensitivity, and to incorporate these features into functional materials that display the new property. This approach allows the power of molecular evolution to be applied to problems in materials science.
correlate chemical-scale behavior (such as a binding constant) with mechanical behavior (such as the ability to form a gel). In addition to providing a high-level of control over the materials properties, this ability to correlate microscopic and macroscopic behavior allows us to express materials engineering problems in chemical terms. Ultimately, we would like to predict mechanical properties from the dilute-solution behavior of the protein components. Realizing this goal would allow us to use directed evolution to select for proteins with a desired property, such as an altered ligand sensitivity, and to incorporate these features into functional materials that display the new property. This approach allows the power of molecular evolution to be applied to problems in materials science. Toward these goals, we have created a toolbox comprised of hundreds of proteins that reversibly self-assemble with various architectures, binding affinities, and ion sensitivities and we are studying how these materials behave. The movie to the right shows the Ca2+-dependent assembly of a protein-based material viewed using video-microscopy. The dots are fluorescent microspheres added to the sample; as the Ca2+ diffuses from right to left, the particles become embedded as the network forms. Tracking the movement of these particles allows us to determine the rheological properties of the sample.