生物物理

Immovable plants see the light condition precisely to adjust themselves to their environment. For this purpose, plants have acquired a variety of photoreceptors in a wide spectral range from UV-B to far-red light. Phytochrome, a red- and far-red reversible photochromic receptor, regulates photomorphogenetic responses. Cryptochrome, a blue light receptor, plays similar roles to those of phytochrome. Phototropin, a member of LOV blue light receptor families, serves to maximize photosynthetic activities by regulating phototropic responses, chloroplast movements, stomata opening, etc. Furthermore, UVR8 senses UV-B light. Molecular bases for the light-signal reception of these photoreceptors are reviewed.

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Intracellular and extracellular mechanical forces affect the dynamics of actin cytoskeletons, however, the underlying biophysical mechanisms how forces are transduced into changes in the actin dynamics remain largely unknown. We find that activity of the actin severing protein ADF/cofilin negatively depends on tension in the actin filament through tension-dependent binding/unbinding of cofilin to/from the actin filament, thereby relaxed actin filaments are severed whereas tensed ones are not. Here we review the latest knowledge on this phenomenon and discuss its biological impact.

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Diffracted X-ray Tracking (DXT) is one of single molecule techniques for investigating intra-molecule dynamics of functional proteins. In DXT, a nanocrystal is immobilized on a target protein and the trajectory of its diffracted spot is analyzed as the motion of the protein. We advanced the time resolution of this method and refined the analysis procedures in the last 5 years, and the method has been useful especially for cooperative motion analysis in multimeric proteins. In this article, we review the characteristic features and recent progress of DXT.

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Number of a molecule is discrete by its nature. Therefore, when detection sensitivity of analytical methods approaches the single molecule level, one faces the intrinsic discreteness of the measured concentration and number of analytes. An emerging analytical method that employs this intrinsic discreteness is digital counting. When an analyte solution is partitioned into many small reaction compartments, such that each molecule is individually encapsulated into a compartment, the analyte quantification is inevitably digitized; each compartment contains none or one molecule of analyte. When a solution of enzyme or enzyme-conjugated molecule is partitioned into such small reactors with fluorogenic substrate, one can count the number of the molecule as that of fluorescent reactors under an optical microscope. We refer to this strategy as “digital counting”. One of the most successful examples of digital counting is digital ELISA, in which target molecules are individually encapsulated in a water-in-oil droplet after bound to enzyme-conjugated antibody. Although the chemistry of digital ELISA; antibody and enzyme is common to conventional ELISA, the detection sensitivity of digital ELISA is higher than that of conventional ELISA by 4 to 6 orders of magnitude. In this review, we introduce recent achievements in digital ELISA and relevant methods.

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