Reversible Photocontrol of Microtubule Stability by Spiropyran-Conjugated Tau-Derived Peptides

Spatiotemporal modulation of microtubules by light has become an important aspect of the biological and nanotechnological applications of microtubules. We previously developed a Tau-derived peptide as a binding unit to the inside of microtubules. Here, we conjugated the Tau-derived peptide to spiropyran, which is reversibly converted to merocyanine by light, as a reversible photocontrol system to stabilize microtubules. Among the synthesized peptides with spiropyran/merocyanine at different positions, several peptides were bound to the inside of microtubules and stabilized the structures of microtubules. The peptide with spiropyran at the N-terminus induced polymerization and stabilization of microtubules, whereas the same peptide with the merocyanine form did not exert these effects. Reversible formation and dissociation of microtubules were achieved using the peptide with spiropyran conjugated at the N-terminus and irradiation with UV and visible light. Spiropyran-conjugated Tau-derived peptides would be useful for spatiotemporal modulation of microtubule stability through reversible photocontrol of binding.

Encapsulation of Nanomaterials Inside Microtubules by Using a Tau-Derived Peptide

Microtubules (MTs) are tubular cytoskeletons, which are used for the various applications such as active matters and therapeutic targets. Although modification of the exterior surface of MTs is frequently used for functionalization of MTs, there was no approach to introduce molecules inside MTs. We previously developed a unique peptide binding to the inner surface of MT, which is derived from a MT-associated protein, Tau. The Tau-derived peptide (TP) can be used to introduce various nanomaterials inside MTs. Here we describe the TP-based encapsulation of fluorescent dye, gold nanoparticle, green fluorescent protein, and magnetic CoPt nanoparticles inside MTs.

Live-Cell Fluorescence Imaging of Microtubules by Using a Tau-Derived Peptide

Microtubules (MTs) are important targets for imaging in living cells because of their vital roles in cellular processes. The dynamics (polymerization/depolymerization) of MTs has been imaged in living cells by utilizing MT-targeted drugs as scaffolds. We previously developed a unique MT-binding motif derived from a MT-associated protein, Tau. The Tau-derived peptide (TP) binds to the inner surface of MTs without inhibiting the dynamics of MTs. We introduce a new protocol for live-cell imaging of MTs by using fluorescently labeled TP. We exemplify that tetramethylrhodamine (TMR)-labeled TP (TP-TMR) is spontaneously internalized into HepG2 cells and binds to intracellular MTs, enabling visualization of MTs in living cells. TP-TMR shows no apparent effects on polymerization/depolymerization of MTs and no cytotoxicity. Thus, the peptide-based approach is useful for long-term imaging of MTs.

Magnetic Force-Induced Alignment of Microtubules by Encapsulation of CoPt Nanoparticles Using a Tau-Derived Peptide

Construction of magnetotactic materials is a significant challenge in nanotechnology applications such as nanodevices and nanotransportation. Artificial magnetotactic materials can be designed from magnetotactic bacteria because these bacteria use magnetic nanoparticles for aligning with and moving within magnetic fields. Microtubules are attractive scaffolds to construct magnetotactic materials because of their intrinsic motility. Nonetheless, it is challenging to magnetically control their orientation while retaining their motility by conjugating magnetic nanoparticles on their outer surface. Here we solve the issue by encapsulating magnetic cobalt-platinum nanoparticles inside microtubules using our developed Tau-derived peptide that binds to their internal pockets. The in situ growth of cobalt-platinum nanoparticles resulted in the formation of a linear-chain assembly of nanoparticles inside the microtubules. The magnetic microtubules significantly aligned with a high order parameter (0.71) along the weak magnetic field (0.37 T) and showed increased motility. This work provides a new concept for designing magnetotactic materials.