Crystal Structures of the Synechocystis Photoreceptor Slr1694 Reveal Distinct Structural States Related to Signaling

摘要

Crystal structures of the Synechocystis BLUF phototaxis photoreceptor Slr1694 have been solved 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 tertiary structures that differ in length of the 5^th beta strand and in 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 occupancy of the hydrophobic Trp binding pocket with a nearby Met. These different tertiary structures may be associated with absorption in the blue region of the spectrum.