Biomod/2011/Columbia/MotorProTeam:Background Information

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Our research focused on applying kinesin motor proteins and microtubules to initiate transport of cargo on a sub-cellular scale. We aimed to create a structure that utilizes multiple microtubules as a foundation for a molecular transport system.

Microtubules are polymers of α and β tubulin heterodimers. Under proper conditions, they polymerize into microtubules. Microtubules are tubular molecules approximately 25 nm in diameter and have lengths ranging from 2 to 20 μm. The ends of the microtubules are polarized depending on whether the terminal subunit is an α or β tubulin monomer (with the end exposing the β subunit as the plus end). The structure of the cytoskeleton and the process of mitosis depend on microtubules.

Kinesin is a type of motor protein that can walk along microtubules. Kinesin is composed of two tightly intertwined tail domains that terminate in two globular motor domain "heads". Using one molecule of adenosine triphosphate per step, they "walk" towards the positive end of a microtubule.

Kinesin and dynein on a microtubule (Hess, Bachand, and Vogel, 2004)
An example of microtubule motility on two kinesin motor proteins. Microtubule length not to scale.

The current method of cargo transport using motor proteins uses unorganized individual microtubules on a kinesin coated surface. Individual cargo-laden microtubules can rotate about their long axis as the glide, dragging and sometimes releasing their cargo. Our proposed transport system would make use of a fleet of micro scale structures each connected to multiple microtubules underneath. A larger structure would have a greatly increased transport efficiency, given that the transport structure would not drag any cargo. Furthermore, using the combined force of multiple microtubules could potentially help carry larger cargo.

Soft lithography is a method of creating nano-scale structures out of polydimethylsiloxane (PDMS) or other polymers. Microtransfer molding (a subset of all soft lithographic processes) involves creating a PDMS mold from a silicon wafer patterned with photoresist. Cavities in the mold are filled with another polymer (in our case, polyurethane) and the mold is placed features down on another surface. Curing (either by heat or UV exposure) causes the liquid polymer to adhere to this new surface, creating the desired microstructures.