Illuminating biological processes with chemistry
Our laboratory has two main objectives: 1) non-invasive optical imaging of the intracellular environment with fluorescence and bioluminescence, and 2) spatial and temporal control over protein function. To achieve these goals, we synthesize small molecules that absorb and/or emit light.
Fluorescent molecules. Study of the intracellular environment using fluorescence is limited by the inherent absorbance of living tissues. Most optical probes in use today absorb and emit light in the visible wavelength region. Absorption of visible wavelength light by cellular components (e.g., flavins, porphyrins) generates excited state molecules that can give rise to background fluorescence and phototoxicity. In whole animals such as the mouse, absorption of light by the hemoglobin in blood is so great that visible wavelength fluorescence is not viable for imaging.
Living tissue is most transparent to light beyond the visible range, in a spectral region known as the near-IR (650-900 nm). Although this is the ideal spectral window for any optical probe of living cells or organisms, most near-IR fluorophores are unsuitable for use in the intracellular environment because they either lack cell-permeability or give high-background labeling of cellular organelles and membranes. One of our major goals is the design and application of new near-IR fluorophores and probes that can freely enter living cells and facilitate studies of specific intracellular events.
Bioluminescent molecules. Luciferase-catalyzed light emission can also be used to report on the intracellular environment, and can be used in live animals such as the mouse. Nonetheless, the properties of luciferase are inherently limited by the ability of the luciferin substrate to access the luciferase, and by its photophysical properties (e.g., emission wavelength). Work in our lab is directed toward the development and optimization of luciferases and luciferins for applications ranging from high-throughput screening to bioluminescence imaging in mice.
To exert spatial and temporal control over cellular processes, our lab is using the power of chemistry to synthesize molecules that can block the activation and interactions of specific proteins. Upon irradiation with light, these molecules either fall apart or rearrange to restore protein function. For example, the location and timing of GTPase activation is critical for proper cell function, but is still poorly understood. We will use this photoactivation approach to study these rapid processes in living cells using fluorescence microscopy.