Takashi Kamei

Complete ON/OFF photoswitching of the motility of a nanobiomolecular machine.

To apply motor proteins as natural nanomolecular machines to transporting systems in nanotechnology, complete temporal control over ON/OFF switching of the motility is necessary. We have studied the photoresponsive inhibition properties of azobenzene-tethered peptides for regulation of kinesin-microtubule motility. Although a compound containing a peptide having an amino acid sequence derived from the kinesins C-terminus (a known inhibitor of kinesins motor domain) and also featuring a terminal azobenzene unit exhibited an inhibition effect, the phototunability of this behavior upon irradiation with UV or visible light was only moderate. Unexpectedly, newly synthesized peptides featuring the reverse sequence of amino acids of the C-terminus of kinesin exhibited excellent photoresponsive inhibition. In particular, azobenzene-CONH-IPKAIQASHGR completely stopped and started the motility of kinesin-microtubules in its trans- and cis-rich states, respectively, obtained after irradiation with visible and UV light, respectively. A gliding motility system containing this photoresponsive inhibitor allowed in situ control of the motion of microtubules on a kinesin-coated glass substrate. It is expected that the present results on the photoresponsive nanomotor system open up new opportunities to design nanotransportation systems.

Dynamic Photocontrol of the Gliding Motility of a Microtubule Driven by Kinesin on a Photoisomerizable Monolayer Surface

The gliding motility of microtubules driven by kinesin on the surface of an azobenzene monolayer presenting lysine terminal groups is reversibly and repeatedly altered upon photoisomerization of the monolayer.

A non-nucleoside triphosphate for powering kinesin-microtubule motility with photo-tunable velocity

Three non-nucleoside triphosphates, one containing an azobenzene moiety, power a kinesin-microtubule system with high motile activity, with an observed maximum velocity of almost half of that obtained with ATP. The cis-trans photoisomerization of the azobenzene unit allows reversible and repeated control over the motile properties of kinesin.

Visible-Light Photocontrol of (E)/(Z) Isomerization of the 4-(Dimethylamino)azobenzene Pseudo-Nucleotide Unit Incorporated into an Oligonucleotide and DNA Hybridization in Aqueous Media

We demonstrate significant photoresponsivity in aqueous media to visible light of pseudo-oligonucleotides possessing 4-(dimethylamino)azobenzene (4-DMAzo) side chains. The spectrum of the 4-DMAzo moiety during 436 nm light irradiation at pH >9 was clearly different from that of the all (E)-form, indicating the presence of the (Z)-form. Thermal (Z)-to-(E) recovery isomerization was faster at pH 9 (k Z -E = ∼101 s−1) than at pH 11; however, addition of 50% ethanol significantly slowed the thermal recovery isomerization at pH 9 (k Z -E = ∼2 s−1) and increased the magnitude of the spectral changes. Significant photoregulation of DNA hybridization by visible light was demonstrated under this condition.

Three approaches to assembling nano-bio-machines using molecular motors

Efforts to use protein molecular motors as nanoactuators are making rapid progress. For instance, it is now possible to carry out directional transport of small cargo along microtracks or microchannels using kinesin-microtubule systems, which could be the basis of micro-conveyor belts or molecular shuttles. However, the applicability of protein-based devices is limited by their poor stability in artificial environments. In addition, assembly of complex, intelligent microdevices or systems will likely require bottom-up self-assembly, and we still do not have sufficient knowledge to rationally design self-assembling protein-based microdevices or systems. One approach to solving the problems associated with protein-based systems is to use DNA-based nanodevices, which are amenable to rational design. Indeed, ingenious design has enabled realization of DNA-based nanoactuators and self-assembled micropatterns of various shapes. One also could use cells, organelles, or tissues as preassembled motile units, and several motile devices have already been realized using this approach. In addition to being less prone to the assemaly problems, cell-based microdevices have the advantage that the motile units reproduce themselves, and genetically encoded functional modifications can be replicated effortlessly. These protein-based, DNA-based, and cell-based systems each have distinct advantages and disadvantages, so that hybrid devices combining the best characteristics of all three would seem the most likely to succeed.

Dynamic photo-control of kinesin on a photoisomerizable monolayer – hydrolysis rate of ATP and motility of microtubules depending on the terminal group

The reversibly and repeatedly altered gliding motility of microtubules driven by kinesin on the photoresponsive monolayer surface is studied. It was confirmed that an azobenzene monolayer surface needs to have free amino terminal groups for the successful dynamic control of the motility of microtubule. The surface of the azobenzene monolayer with terminal amino groups can dynamically control the ATP hydrolysis activity of kinesin which resulted in the change in motility of the microtubules.