University of California, Merced
Victor Muñoz, Mourad Sadqi, Zifan Wang
A major challenge in biosensor research is to achieve specific sensing at nanoscale (molecular) resolutions in living cells and in real time. Proteins would be ideal scaffolds because of their high specificity and tunable affinity for binding, and their built-in mechanism for transducing signals through conformational changes. However, reaching nanoscale resolution in real time requires single-molecule devices that produce analog outputs. This is a serious limitation because typical proteins behave as molecular switches with inherently binary outputs: in the presence of a specific molecule to which a protein binds tightly, the unfolded protein folds to its correct conformation and produces a signal such as fluorescence; whereas in the absence of the ligand molecule the protein unfolds and the signal stops altogether. A team of investigators at University of California, Merced proposes to develop single-molecule biosensors based on their previous discovery of “downhill folding” proteins, i.e., proteins that fold and unfold gradually through a continuum of partially-folded intermediates not separated by free-energy barriers. These proteins are theoretically and computationally predicted to detect other molecules in an analog mode, much like a rheostat. The team plans to apply the “folding coupled to binding” biosensor-design principle to proteins purposely engineered to fold downhill and implement them with gradual fluorescent signals. These novel sensors are expected to display wide dynamic range, ultrafast response and analog readouts at the single molecule level. To implement this idea, the team will employ a multidisciplinary approach that combines protein engineering and design, single-molecule fluorescence microscopy, nuclear magnetic resonance, theoretical modeling, and high-performance computational methods.
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