Microtransporters using cargo-laden microtubules propelled by kinesin motors are attractive for numerous applications in nanotechnology. To improve the efficiency of transport, the movement of microtubules must be guided by microfabricated tracks. However, the mechanisms of the guiding methods used are not fully understood. Here, using computer simulation, we systematically studied the guiding of such microtransporters by three different types of guiding methods: a chemical boundary, a physical barrier, and their combination. The simulation reproduced the probabilities of guiding previously observed experimentally for the three methods. Moreover, the simulation provided further insight into the mechanisms of guiding, which overturn previous assumptions and models.
We present a simulation study of an actomyosin in vitro motility assay. In vitro motility assays have served as an essential element facilitating the application of actomyosin in nanotechnology; such applications include biosensors and biocomputation. Although actomyosin in vitro motility assays have been extensively investigated, some ambiguities remain, as a result of the limited spatio-temporal resolution and unavoidable uncertainties associated with the experimental process. These ambiguities hamper the rational design of nanodevices for practical applications. Here, with the aim of moving toward a rational design process, we developed a 3D computer simulation method of an actomyosin in vitro motility assay, based on a Brownian dynamics simulation. The simulation explicitly included the ATP hydrolysis cycle of myosin. The simulation was validated by the reproduction of previous experimental results. More importantly, the simulation provided new insights that are difficult to obtain experimentally, including data on the number of myosin motors actually binding to actin filaments, the mechanism responsible for the guiding of actin filaments by chemical edges, and the effect of the processivity of motor proteins on the guiding probabilities. The simulations presented here will be useful in interpreting experimental results, and also in designing future nanodevices integrated with myosin motors.
Motor protein kinesin has been utilized as nanoand microscale material transport system (so-called molecular shuttles driven by kinesin motors). Successful transports rely on guidance of molecular shuttles movements with microfabricated guiding tracks. Predictions of guiding probability at the boundaries are important in designing microfabricated tracks. In this study, we computed the guiding probabilities for three different guiding tracks with our simulation:(1) tracks with selective absorption of kinesins (chemical tracks); (2) tracks with microfabricated guiding walls covered with kinesins (topographic tracks); and (3) tracks with microfabriacted guiding wall without adsorption of kinesins (combined tracks). We reproduced experimental guiding probabilities qualitatively, and revealed mechanisms of the guidance and the dissociation of the shuttles at the boundary by visualizing the movements of the microtubules with a three-dimensional simulation.
Fish melanocytes change their appearances through aggregations and dispersions of melanosomes, corresponding to bright and dark, respectively. Here, we have envisioned an optical microdevice which changes its color through self-organizations of microtubules and kinesins. Formations and disassemblies of microtubule asters lead to aggregations and dispersions of kinesin-streptavidin complexes, which are "melanosomes" in the device. We investigated the feasibility of the device with a computer simulation. The simulation showed that the kinesinstreptavidin complexes initially distributed all over the chamber could be accumulated at the center of the aster. With the computer simulation, we will show guidelines for the design of the envisioned optical device. 1P315Theree We have developed an on-chip multi-imaging flow cytometer system for a real-time bright field/fluorescent dual-image analysis. The system consists of (1) a disposable microfluidic chip, (2) a bright field/fluorescent dualimage microscopic optical system, and (3) a real-time high-speed digital camera with image-processing function. For the high-speed image acquisition, we adopted single-band width LED light sauce, synchronized with camera shutter intervals, and FPGA circuit was directly connected to the camera part. Using this system, we analyzed not only shapes of cell, but also nuclei formation with faster than 1/200 s. In this meeting, we introduce the potential and possibilities of this system and the new index of cell identification, 'imaging biomarkers'.-S158 - The fundamental chromatin packing unit in eukaryotes is the nucleosome. Prior single-molecule experiments have exerted linear tension to stretch both chromatin fibers and mononucleosome, which have given information on the nature of the free-energy barrier for a particular disruption pathway.We develop a theoretical model including torsional constraints, which suggests that the disruption pathway may be sensitive to the torsional loading of the nucleosome. Experimentally we apply force and torque simultaneously to disrupt a mononucleosome using an optical torque wrench. Positive supercoiling is found to destabilize the nucleosome while negative supercoiling has little effect, which is consistent with our model.
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