Web Release Date: October 3,
Crystal Structures of the Synechocystis Photoreceptor Slr1694 Reveal Distinct
Structural States Related to Signaling
and
Department of Biology, Indiana University, Bloomington, Indiana 47405, Consortium for Advanced Radiation Sources, Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, and Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan
Received July 15, 2006
Revised Manuscript Received August 31, 2006
Abstract:
Crystal structures of the Synechocystis BLUF phototaxis photoreceptor Slr1694 have been
determined in two crystal forms, a monoclinic form at 1.8 Å resolution and an orthorhombic form at 2.1
Å 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 tertiary
structures that differ in the length of the fifth 
-strand and in the orientation of Trp91, a conserved Trp
residue near the FMN chromophore. Fluorescence spectroscopic analysis on Slr1694 in solution is consistent
with motion of Trp91 from a hydrophobic environment in the dark state to a more hydrophilic environment
in the light-excited state. Mutational analysis indicates that movement of Trp91 is dependent on the
occupancy of the hydrophobic Trp binding pocket with a nearby Met. These different tertiary structures
may be associated with absorption changes in the blue region of the spectrum.
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