The Transcription Factor Ultrabithorax Forms Extensible, Hierarchically Ordered Assemblies that are Readily Functionalized by Gene Fusion

Abstract

Proteins that naturally self-assemble to form materials are often challenging to produce as recombinant proteins, and require harsh conditions to instigate assembly in vitro, limiting their ability to be engineered for specific applications. Surprisingly, the Drosophila melanogaster Hox protein Ultrabithorax (Ubx) readily self-assembles in vitro in mild buffers, even though this protein does not form large aggregates as part of its native function. Ubx hierarchically associates to form materials that are ordered on the nanoscale to macroscale. The mechanical properties of Ubx fibers are tunable, and fibers can be constructed with a similar breaking stress and strain as natural elastin. Because Ubx self-assembles within hours in a mild buffer, other proteins can be incorporated into Ubx materials via gene fusion without compromising the ability of Ubx to assemble, or the functionality of the appended protein. A variety of proteins have successfully been incorporated into Ubx materials, ranging in structure, size, and charge. These functions can be easily patterned within the materials. This strategy has been used to control the behavior of cells in culture.