Future

Conclusion and Future Application

During our summer project, we achieved the following: 

1. Actin did not polymerize spontaneously in solution.

2. Actin polymerized into a fibrous structure. 

These were achieved by binding Modified Thymosin to Actin and maintaining it in solution, Actin remained as monomers without polymerizing in solution. In addition, it was confirmed through experiment that actin polymerized into a fibrous structure.

However, there were some uncompleted aspects of the project within the timeframe. Those concepts will be introduced, along with the functions we wish to implement, using brief descriptions and diagrams.

Polymerization Activator

Actin monomers bond to Modified Thymosin do not polymerize and remain as monomers in solution; in this state, they do not self-organize into fibrous Actin. Therefore, it is necessary to remove the Modified Thymosin, which inhibits binding, to allow actin to enter a polymerizable state. We believe that by using a Polymerization Activator that acts more strongly on actin than Modified Thymosin and promotes polymerization, Actin can be induced to polymerize and self-organize into a fibrous structure.

The requirements for a Polymerization Activator include: 

1. Stronger affinity towards Actin than Modified Thymosin to promote polymerization.

2. Higher functionality to not affect other components, such as BASE and TARGET, and not self-organize into structures.

3. Simpler structure to facilitate molecular modification tailored to the system.

4. High compatibility with biological systems for the consideration of in vivo applications.

Increase the number of connections between BASE and TARGET

It further hypothesizes that by polymerizing many fibrous actin strands between TARGET and BASE, the overall rigidity of the fibrous actin structure will increase, allowing a stable connection between TARGET and BASE. Since fibrous actin is self-organized by Polymerization Activators, increasing the number of fibrous actin strands can likely be achieved at an early stage. To polymerize a large number of fibrous actin strands, it is considerably necessary to increase the number of actin molecules that directly bind to TARGET and BASE. 

Control the distance between BASE and TARGET

Our ultimate goal is to capture TARGET by connecting and drawing it closer towards BASE. To achieve this, it requires a mechanism to gradually shortens the length of fibrous Actin that links BASE and TARGET while maintaining its fibrous shape. Implementing this mechanism requires not only designing Actin monomers that more readily undergo polymerization and depolymerization, but also devising an irreversible reaction system to eliminate actin and prevent re-polymerization, ensuring that the length of fibrous Actin does not revert.

If the polymerization and depolymerization of fibrous Actin can be controlled responsively and precisely, this system could be used as a new device utilizing molecular motors. By regulating the number of actin polymers connecting BASE and TARGET in a fibrous state, it would become possible to control the distance between BASE and TARGET. To realize such a system, it is essential to implement a mechanism that detaches the Polymerization Activator from actin molecules with the Polymerization Activator attached, reattaches Thymosin, and prevents unintended re-polymerization. This would ensure that the reaction proceeds swiftly and reliably. 

Practical use

Actin and Thymosin are abundantly present within living organisms, and we believe that the system we propose has high biocompatibility. The system to connects BASE and TARGET and draw TARGET closer has potential applications as follows: 

For example, there is unwanted waste products occuring within a biological body, needing a cleaner to collect and remove out this waste; by considering this waste as TARGET and the cleaner as BASE, this proposed system could facilitate the collection and removal of waste within cells and tissues, aiding its expulsion from the body. One advantage of using this system for waste removal is that many fibrous actin molecules can bind to one single BASE, enabling the collection of a large amount of waste at once.

Furthermore, if a grab-and-release mechanism can be further incorporated into the system–allowing a broader selection of materials for TARGET to capture–it might function as a robotic arm within the nanoscale to microscale world of cells and tissues. This could enable it to act as a construction robot, performing tasks like installing microtubules, akin to plumbing work.