Biological sensors: More than one way to sense oxygen

International audienceRecently determined structures of the oxygen-sensing heme domain of the bacterial protein FixL have revealed a new binding environment and signal transduction mechanism for heme; they have also provided new insights into the diverse 'PAS' domain superfamily

Structural tuning of the fluorescent protein iLOV for improved photostability

Background: iLOV is a fluorescent flavoprotein engineered from the plant blue light receptor phototropin. <p/>Results: Structures reveal altered protein-chromophore interactions within the flavin-binding cavity of iLOV when compared with its progenitors. Directed evolution further anchored the chromophore to increase iLOV photostability by an order of magnitude. <p/>Conclusion: Improving iLOV photostability by constraining its fluorophore establishes a framework for fine-tuning fluorescence. <p/>Significance: Enhanced photostability increases iLOV utility as an oxygen-independent fluorescent reporter

Plant UVR8 photoreceptor senses UV-B by tryptophan-mediated disruption of cross-dimer salt bridges

The recently identified plant photoreceptor UVR8 triggers regulatory changes in gene expression in response to ultraviolet-B (UV-B) light via an unknown mechanism. Here, crystallographic and solution structures of the UVR8 homodimer, together with mutagenesis and far-UV circular dichroism spectroscopy, reveal its mechanisms for UV-B perception and signal transduction. +¦-propeller subunits form a remarkable, tryptophan-dominated, dimer interface stitched together by a complex salt-bridge network. Salt-bridging arginines flank the excitonically coupled cross-dimer tryptophan pyramidresponsible for UV-B sensing. Photoreception reversibly disrupts salt bridges, triggering dimer dissociation and signal initiation. Mutation of a single tryptophan to phenylalanine retunes the photoreceptor to detect UV-C wavelengths. Our analyses establish how UVR8 functions as a photoreceptor without a prosthetic chromophore to promote plant development and survival in sunlight