Japanese researchers successfully produced “magnetic microtubules” inspired by magnetotactic bacteria
The research team of Assistant Professor Inaba and Professor Matsuura Kazunori of the Department of Chemical Biology, Faculty of Engineering, Tottori University, Japan, and the research team of Associate Professor Kakugoaki and Professor Sada Kazuki of the Graduate School of Science, Hokkaido University, through By introducing magnetic nanoparticles into the interior of “microtubules,” protein nanotubular aggregates, the world’s first successful fabrication of “magnetic microtubules” that can be aligned under the influence of magnets (Fig. 1).
Figure 1: Study concept map.
By introducing cobalt-platinum (CoPt) nanoparticles into the microtubules, the microtubules are aligned along the magnetic field of the magnet.
It is known that there are magnetotactic bacteria with magnetic nanoparticles in the body in nature, which will move along the geomagnetic field. Although the industry is developing magnetic materials that imitate magnetotactic bacteria, it is difficult to balance “magnetic field responsiveness” and “mobility”. This study focuses on the protein nanotubes with mobility—microtubules. Using the self-developed Tau-derived peptide TP that can bind to the inside of microtubules, a magnetic cobalt-platinum (CoPt) nanotube was successfully introduced into the microtubules. particles. The study found that the microtubules containing CoPt nanoparticles will respond to the neodymium magnets sold in hundred yuan stores and arrange them very regularly, and the original mobility of the microtubules will not decrease, but will increase. This achievement is expected to be used as a method for controlling the motion direction of ultra-small devices composed of microtubules and molecular robots.
Naturally occurring magnetotactic bacteria use their large arrays of magnetic nanoparticles (magnetosomes) as a compass to determine the direction of motion (Fig. 2). If a magnetic material that can move in response to this magnetic field can be realized, it is expected to be used as an extremely small molecular device and a molecular robot. However, it is extremely difficult to develop materials that take into account both “magnetic field responsiveness” and “mobility”. Microtubules, part of the cytoskeleton, are protein nanotubes known to move on substrates immobilized with motor proteins, and are “motile” but not “magnetic field responsive.” Previously, there were cases of development of magnetic nanoparticles on the outer surface of microtubules, but there was a major problem that the nanoparticles bound to the surface inhibited the interaction between motor proteins and microtubules, resulting in a significant decrease in the movement speed of microtubules . The research team believes that if magnetic nanoparticles can be introduced into the “inside of microtubules” like magnetotactic bacteria, they can have both “magnetic field responsiveness” and “mobility”. Therefore, this study used the self-developed microtubule internal binding peptide to successfully fabricate microtubules containing magnetic nanoparticles for the first time in the world, and found that such microtubules can be arranged in an orderly manner in response to a magnet, and their mobility is enhanced.
Figure 2: Magnetotactic bacteria and their movement along the geomagnetic field
The research team first linked the Tau-derived peptide TP bound to the inside of microtubules and the peptide that promotes the formation of magnetic nanoparticles—CoPt nanoparticles, synthesized CBP-TP, and combined it with tubulin (a constituent component of microtubules) labeled with a red fluorescent dye. )complex. Then, microtubules containing CoPt nanoparticles were fabricated using 2 methods (Fig. 3a).
The Before method first adds Co ions and Pt ions, and then adds the reducing agent sodium borohydride (NaBH4), thereby synthesizing CoPt nanoparticles on tubulin, and then adding GTP to simulate GMPCPP to make microtubules. The “After” method first adds GMPCPP to make microtubules, and then synthesizes CoPt nanoparticles inside the microtubules. Observation with a transmission electron microscope (TEM) confirmed that the CoPt nanoparticles were isolated inside the microtubules fabricated by the “Before” method, and the CoPt nanoparticles were partially arranged continuously inside the microtubes fabricated by the “After” method (Fig. 3b) .
Figure 3: (a) Fabrication of microtubes containing CoPt nanoparticles and (b) transmission electron microscopy (TEM) images.
Black dots with white arrows indicate CoPt nanoparticles.
The research team immobilized the obtained microtubes containing CoPt nanoparticles on a substrate in the presence of a commercially available neodymium magnet with a magnetic flux density of 0.37T (Tesla), and found that the microtubes produced by the “After” method Along the direction of the magnetic field (horizontal direction) are arranged very regularly (Figure 4). Generally speaking, in order to align magnetic materials, a magnetic field above 10T is required. It is a very interesting result that micropipes are aligned with such a weak magnetic field.
(a) Alignment of CoPt nanoparticles-containing microtubules in the presence of a neodymium magnet.
(b) Top: Confocal laser fluorescence microscopy images of CoPt nanoparticles-containing microtubules fabricated by the “After” method with and without a magnetic field. Arrows indicate the direction of the magnetic field, and it can be seen that the microtubules are aligned along the direction of the magnetic field.
Bottom: Angular degree distribution in the horizontal direction of microtubules.
On the other hand, the microtubules fabricated by the “Before” method and the microtubules modified with CoPt nanoparticles on the outer surface did not show magnetic field responsiveness. This shows that the continuous arrangement of CoPt nanoparticles inside the microtubes fabricated by the “After” method works like nanowires, enhancing the magnetic field responsiveness. It can be said that this characteristic is similar to natural magnetotactic bacteria. In addition, the analysis of the movement speed of microtubules on the substrate of immobilized molecular motors found that when the outer surface was modified with CoPt nanoparticles, the speed decreased, and the microtubules containing CoPt nanoparticles fabricated by the “After” method were compared with ordinary microtubules. , the speed increased by 1.2 times. Presumably, this is because the rigidity of microtubules is enhanced by the formation of CoPt nanoparticles inside the microtubules.
In this study, by imitating magnetotactic bacteria and using peptides to form CoPt nanoparticles inside the microtubules, magnetic microtubules with both “magnetic field responsiveness” and “mobility” were successfully produced. By using a magnetic field to control the alignment and movement of microtubules in a very small space, it is expected to be applied to ultra-small devices and molecular robots. In particular, if the movement direction of microtubules can be controlled by a magnetic field like magnetotactic bacteria, it is expected to efficiently transport molecules to desired locations and control the collective movement of microtubules.