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Pressure Perturbations of Citrine Structure Lead to a Fluorescence Shift
Presented by:  Buz Barstow, Gruner Group, Cornell

Citrine is a yellow fluorescent protein derived from the Green Fluorescent Protein. Citrine's fluorescence spectrum is sensitive to high pressure; the peak of its spectrum shifts towards the red by approximately 1 nanometer for every one hundred megapascals of applied pressure at room temperature. To investigate the basis of this effect the structure of Citrine has been solved over a range of high pressures using a novel high pressure cryo-cooling technique, and the fluorescence spectra of pressure cryo-cooled solutions have been measured for direct comparison with the pressure cooled crystal structures. The chromophore, the light emitting element in the protein, shows a progressive deformation with increasing pressure, while the spectra of pressure cryo-cooled solutions blue-shifts with increasing cooling pressure. Quantum chemical calculations of the molecular orbitals of these high pressure structures provide an intuitive and quantitative explanation of the fluorescence blue-shift, and demonstrate the sensitivity of this protein's function to sub-Ã…ngstrom deformations in its active site.