Blue light regulates processes such as the development of plants and fungi and the behaviour of microbes. Two types of blue-light receptor flavoprotein have been identified: cryptochromes, which have partial similarity to photolyases, and phototropins, which are photoregulated protein kinases. The former have also been found in animals with evidence of essential roles in circadian rhythms. Euglena gracilis, a unicellular flagellate, abruptly changes its swimming direction after a sudden increase or decrease in incident blue light intensity, that is, step-up or step-down photophobic responses, resulting in photoavoidance or photoaccumulation, respectively. Although these photobehaviours of Euglena have been studied for a century, the photoreceptor molecules mediating them have remained unknown. Here we report the discovery and biochemical characterization of a new type of blue-light receptor flavoprotein, photoactivated adenylyl cyclase, in the photoreceptor organelle of Euglena gracilis, with molecular genetic evidence that it mediates the step-up photophobic response.

Lectin-like, oxidized low-density lipoprotein (LDL) receptor 1, LOX-1, is the major receptor for oxidized LDL (OxLDL) in endothelial cells. We have determined the crystal structure of the ligand binding domain of LOX-1, with a short stalk region connecting the domain to the membrane-spanning region, as a homodimer linked by an interchain disulfide bond. In vivo assays with LOX-1 mutants revealed that the "basic spine," consisting of linearly aligned arginine residues spanning over the dimer surface, is responsible for ligand binding. Single amino acid substitution in the dimer interface caused a severe reduction in LOX-1 binding activity, suggesting that the correct dimer arrangement is crucial for binding to OxLDL. Based on the LDL model structure, possible binding modes of LOX-1 to OxLDL are proposed.

Life on earth relies upon photosynthesis, which consumes carbon dioxide and generates oxygen and carbohydrates. Photosynthesis is sustained by a dynamic environment within the plant cell involving numerous organelles with cytoplasmic streaming. Physiological studies of chloroplasts, mitochondria and peroxisomes show that these organelles actively communicate during photorespiration, a process by which by-products produced by photosynthesis are salvaged. Nevertheless, the mechanisms enabling efficient exchange of metabolites have not been clearly defined. We found that peroxisomes along chloroplasts changed shape from spherical to elliptical and their interaction area increased during photorespiration. We applied a recent femtosecond laser technology to analyse adhesion between the organelles inside palisade mesophyll cells of Arabidopsis leaves and succeeded in estimating their physical interactions under different environmental conditions. This is the first application of this estimation method within living cells. Our findings suggest that photosynthetic-dependent interactions play a critical role in ensuring efficient metabolite flow during photorespiration.