Different Microtubule Structures Assembled by Kinesin Motors

Molecular Machines and Microrobots: Nanoarchitectonics Developments and On-Water Performances

This review will focus on micromachines and microrobots, which are objects at the micro-level with similar machine functions, as well as nano-level objects such as molecular machines and nanomachines. The paper will initially review recent examples of molecular machines and microrobots that are not limited to interfaces, noting the diversity of their functions. Next, examples of molecular machines and micromachines/micro-robots functioning at the air-water interface will be discussed. The behaviors of molecular machines are influenced significantly by the specific characteristics of the air-water interface. By placing molecular machines at the air-water interface, the scientific horizon and depth of molecular machine research will increase dramatically. On the other hand, for microrobotics, more practical and advanced systems have been reported, such as the development of microrobots and microswimmers for environmental remediations and biomedical applications. The research currently being conducted on the surface of water may provide significant basic knowledge for future practical uses of molecular machines and microrobots.

Investigation of the Electrical Properties of Microtubule Ensembles under Cell-Like Conditions

Microtubules are hollow cylindrical polymers composed of the highly negatively-charged (~23e), high dipole moment (1750 D) protein α, β- tubulin. While the roles of microtubules in chromosomal segregation, macromolecular transport, and cell migration are relatively well-understood, studies on the electrical properties of microtubules have only recently gained strong interest. Here, we show that while microtubules at physiological concentrations increase solution capacitance, free tubulin has no appreciable effect. Further, we observed a decrease in electrical resistance of solution, with charge transport peaking between 20-60 Hz in the presence of microtubules, consistent with recent findings that microtubules exhibit electric oscillations at such low frequencies. We were able to quantify the capacitance and resistance of the microtubules (MT) network at physiological tubulin concentrations to be 1.27 × 10^-5 F and 9.74 × 10⁴ Ω. Our results show that in addition to macromolecular transport, microtubules also act as charge storage devices through counterionic condensation across a broad frequency spectrum. We conclude with a hypothesis of an electrically tunable cytoskeleton where the dielectric properties of tubulin are polymerisation-state dependent.

Fluorescent Tau-derived Peptide for Monitoring Microtubules in Living Cells

Microtubules (MTs) are key cytoskeletal components that modulate various cellular activities with their dynamic structural changes, including polymerization and depolymerization. To monitor the dynamics of MTs in living cells, many drug-based fluorescent probes have been developed; however, these also potentially disturb the polymerization/depolymerization of MTs. Here, we report nondrug, peptide-based fluorescent probes to monitor MTs in living cells. We employed a Tau-derived peptide (TP) that has been shown to bind MTs without inhibiting polymerization/depolymerization in vitro. We show that a tetramethylrhodamine (TMR)-labeled TP (TP-TMR) is internalized into HepG2 cells and binds to intracellular MTs, enabling visualization of MTs as clear, fibrous structures. The binding of TP-TMR shows no apparent effects on polymerization/depolymerization of MTs induced by MT-targeted drugs and temperature change. The main uptake mechanism of TP-TMR was elucidated as endocytosis, and partial endosomal escape resulted in the binding of TP-TMR to MTs. TP-TMR exhibited no cytotoxicity compared with MT-targeted drug scaffolds. These results indicate that TP scaffolds can be exploited as useful MT-targeted tools in living cells, such as in long-term imaging of MTs.