09. A Bacterium’s Cooperative Lattice
(l.) Brian Crane, (r.) Jack Freed
Brian Crane and Jack H. Freed, Chemistry and Chemical Biology, and their research labs have begun to unravel the molecular details of how cell-surface receptors and transducing enzymes assemble to detect, integrate, and process chemical signals. Bacteria sense minute changes in their chemical environment (as small as 0.1 percent in molecular concentrations) over a large dynamic range (five orders of magnitude in nutrient concentration). Crane and Freed discovered that receptors assemble into a cooperative lattice on a bacterium’s surface to amplify these infinitesimal changes in the environment and start the processes that lead to specific responses within the cell. Combining x-ray crystallography for determining the structure of receptors and enzymes with pulsed electron-spin resonance (ESR) techniques for measuring interactions between them, the researchers developed a structural model showing how the complex of receptors is organized. They believe that the kind of cooperative lattice on the surface of a bacterium may point to a general mechanism for cellular signaling, which could inspire the development of molecular devices. Such devices might sense a wide range of chemical, light, ionic strength (salt), pH, and heavy metals with great sensitivity, gain, and dynamic range.