| Abstract
| - Crystal structures of the Synechocystis BLUF phototaxis photoreceptor Slr1694 have beendetermined in two crystal forms, a monoclinic form at 1.8 Å resolution and an orthorhombic form at 2.1Å resolution. In both forms, the photoreceptor is comprised of two pentamer rings stacked face to face.Twenty total subunits in the two asymmetric units of these crystal forms display three distinct tertiarystructures that differ in the length of the fifth β-strand and in the orientation of Trp91, a conserved Trpresidue near the FMN chromophore. Fluorescence spectroscopic analysis on Slr1694 in solution is consistentwith motion of Trp91 from a hydrophobic environment in the dark state to a more hydrophilic environmentin the light-excited state. Mutational analysis indicates that movement of Trp91 is dependent on theoccupancy of the hydrophobic Trp binding pocket with a nearby Met. These different tertiary structuresmay be associated with absorption changes in the blue region of the spectrum.
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